diff --git a/src/gfxinit.cpp b/src/gfxinit.cpp
index 754ce12f82..9149ee915e 100644
--- a/src/gfxinit.cpp
+++ b/src/gfxinit.cpp
@@ -42,21 +42,14 @@ static const SpriteID * const _landscape_spriteindexes[] = {
 	_landscape_spriteindexes_toyland,
 };
 
-/** file index of first user-added GRF file */
-int _first_user_grf_file_index;
-int _opengfx_grf_file_index;
-int _progsig_grf_file_index;
-
 /**
  * Load an old fashioned GRF file.
  * @param filename   The name of the file to open.
  * @param load_index The offset of the first sprite.
  * @param needs_palette_remap Whether the colours in the GRF file need a palette remap.
- * @return The number of loaded sprites.
  */
-static uint LoadGrfFile(const char *filename, uint load_index, bool needs_palette_remap)
+static SpriteFile &LoadGrfFile(const char *filename, uint load_index, bool needs_palette_remap)
 {
-	uint load_index_org = load_index;
 	uint sprite_id = 0;
 
 	SpriteFile &file = OpenCachedSpriteFile(filename, BASESET_DIR, needs_palette_remap);
@@ -81,7 +74,7 @@ static uint LoadGrfFile(const char *filename, uint load_index, bool needs_palett
 	}
 	DEBUG(sprite, 2, "Currently %i sprites are loaded", load_index);
 
-	return load_index - load_index_org;
+	return file;
 }
 
 /**
@@ -176,8 +169,8 @@ static void LoadSpriteTables()
 	LoadGrfFile(used_set->files[GFT_BASE].filename, 0, PAL_DOS != used_set->palette);
 
 	/* Progsignal sprites. */
-	//_progsig_grf_file_index = i;
-	LoadGrfFile("progsignals.grf", SPR_PROGSIGNAL_BASE, false);
+	SpriteFile &progsig_file = LoadGrfFile("progsignals.grf", SPR_PROGSIGNAL_BASE, false);
+	progsig_file.flags |= SFF_PROGSIG;
 
 	/* Fill duplicate programmable pre-signal graphics sprite block */
 	for (uint i = 0; i < PROGSIGNAL_SPRITE_COUNT; i++) {
@@ -264,17 +257,6 @@ static void LoadSpriteTables()
 	 * Let's say everything which provides less than 500 sprites misses the rest intentionally. */
 	if (500 + _missing_extra_graphics > total_extra_graphics) _missing_extra_graphics = 0;
 
-	//_first_user_grf_file_index = i + 1;
-	//_opengfx_grf_file_index = -1;
-	for (GRFConfig *c = master; c != nullptr; c = c->next) {
-		if (c->status == GCS_DISABLED || c->status == GCS_NOT_FOUND || HasBit(c->flags, GCF_INIT_ONLY)) continue;
-		if (c->ident.grfid == BSWAP32(0xFF4F4701)) {
-			/* Detect OpenGFX GRF ID */
-			//_opengfx_grf_file_index = index;
-			break;
-		}
-	}
-
 	/* Free and remove the top element. */
 	delete extra;
 	delete master;
diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index 60ad30d474..cea70af355 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -10014,7 +10014,10 @@ void LoadNewGRFFile(GRFConfig *config, GrfLoadingStage stage, Subdirectory subdi
 		SpriteFile temporarySpriteFile(filename, subdir, needs_palette_remap);
 		LoadNewGRFFileFromFile(config, stage, temporarySpriteFile);
 	} else {
-		LoadNewGRFFileFromFile(config, stage, OpenCachedSpriteFile(filename, subdir, needs_palette_remap));
+		SpriteFile &file = OpenCachedSpriteFile(filename, subdir, needs_palette_remap);
+		LoadNewGRFFileFromFile(config, stage, file);
+		file.flags |= SFF_USERGRF;
+		if (config->ident.grfid == BSWAP32(0xFF4F4701)) file.flags |= SFF_OGFX;
 	}
 }
 
diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index 4986c012fa..35ce00f49b 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -2630,17 +2630,15 @@ void DrawSingleSignal(TileIndex tile, const RailtypeInfo *rti, Track track, Sign
 			sprite = SPR_PROGSIGNAL_BASE + 16 + image * 2 + condition;
 		}
 
-		extern int _progsig_grf_file_index;
-		//is_custom_sprite = (int) GetOriginFileSlot(sprite) != _progsig_grf_file_index;
+		SpriteFile *file = GetOriginFile(sprite);
+		is_custom_sprite = !(file != nullptr && file->flags & SFF_PROGSIG);
 	} else {
 		/* Normal electric signals are stored in a different sprite block than all other signals. */
 		sprite = (type == SIGTYPE_NORMAL && variant == SIG_ELECTRIC) ? SPR_ORIGINAL_SIGNALS_BASE : SPR_SIGNALS_BASE - 16;
 		sprite += type * 16 + variant * 64 + image * 2 + condition + (IsSignalSpritePBS(type) ? 64 : 0);
 
-		int origin_slot = 0; //GetOriginFileSlot(sprite);
-		extern int _first_user_grf_file_index;
-		extern int _opengfx_grf_file_index;
-		is_custom_sprite = origin_slot != _opengfx_grf_file_index && (origin_slot >= _first_user_grf_file_index);
+		SpriteFile *file = GetOriginFile(sprite);
+		is_custom_sprite = file != nullptr && (file->flags & SFF_USERGRF) && !(file->flags & SFF_OGFX);
 	}
 
 	if (is_custom_sprite && show_restricted && _settings_client.gui.show_restricted_signal_default && !HasBit(rti->ctrl_flags, RTCF_RESTRICTEDSIG)) {
diff --git a/src/spriteloader/sprite_file_type.hpp b/src/spriteloader/sprite_file_type.hpp
index b7492afade..40eb1fd99d 100644
--- a/src/spriteloader/sprite_file_type.hpp
+++ b/src/spriteloader/sprite_file_type.hpp
@@ -12,15 +12,26 @@
 
 #include "../random_access_file_type.h"
 
+enum SpriteFileFlags : uint8 {
+	SFF_NONE                  = 0,
+	SFF_USERGRF               = 1 << 0,
+	SFF_OGFX                  = 1 << 1,
+	SFF_PROGSIG               = 1 << 2,
+};
+DECLARE_ENUM_AS_BIT_SET(SpriteFileFlags)
+
 /**
  * RandomAccessFile with some extra information specific for sprite files.
  * It automatically detects and stores the container version upload opening the file.
  */
 class SpriteFile : public RandomAccessFile {
+	size_t content_begin;   ///< The begin of the content of the sprite file, i.e. after the container metadata.
 	bool palette_remap;     ///< Whether or not a remap of the palette is required for this file.
 	byte container_version; ///< Container format of the sprite file.
-	size_t content_begin;   ///< The begin of the content of the sprite file, i.e. after the container metadata.
+
 public:
+	SpriteFileFlags flags = SFF_NONE;
+
 	SpriteFile(const std::string &filename, Subdirectory subdir, bool palette_remap);
 	SpriteFile(const SpriteFile&) = delete;
 	void operator=(const SpriteFile&) = delete;