No, you do not use any BGL file for the letters. Step by Step:
For the background square (we'll use yellow):
1. Click the button with the purple shape and G on it (Add Custom Ground Poly):
2. Create the rectangle shape on the ramp apron. Double click at the last vertex.
3. In the GP Editor that pops up, choose as Main Texture gp_Yellow_20F. Leave the Layer as the default 24.
4. Click OK.
5. Adjust the shape/size of the rectangle in ADE, if needed:
5a. Move vertices as needed.
5b. Double click the polygon.
5c. In the GP Editor click the Reset button.
5d. Click OK.
For the lettering (we'll use red lettering, creating the space A3): NOTE: if you really need black lettering, see below.
1. Within the polygon we created above, create a new ground polygon the shape of the letter A on this yellow background.
2. In the GP Editor, set the Layer to 28.
3. Choose as Main Texture gp_Signs_Red. If you need to resize/reshape the polygon in ADE, do this first - click OK and follow step 5 above.
4. Click the left button under Change Color and choose a bright color.
5. Click the left button under Drag.
6. Click on the upper left vertex (it turns red) and drag it to the upper right of the letter A.
7. Repeat 5 until the box is enclosing the letter A. Zoom in as needed using the + button under Zoom.
8. Click OK.
9. Repeat steps 1 to 8 above but creating a polygon where the number 3 should be, and moving the vertices to the number 3 in the texture.
Unfortunately there is no existing texture for black letters, but that can be created relatively easily. NOTE: For the files already created, see the post below this. But this is a very useful technique to learn anyway.
1. Take the gp_Signs_White texture in the Textures_Dpy folder, copy it, paste it, and rename the copy gp_Signs_Black.bmp.
2. In any paint program, load this new image and choose Negative Image (i.e. black to white and white to black).
3. Save the image.
4. In DXTBmp, load the gp_Signs_White.bmp file from the Textures folder. It will contain an alpha channel image in the upper right.
5. Choose Alpha/Export Alpha Channel. Export into a convenient folder, I use the Textures folder. Name it gp_Signs_Black_ALPHA.bmp.
6. Copy our new gp_Signs_Black.bmp file and paste into the Textures folder.
7. In the Textures folder, open our gp_Signs_Black.bmp file into any paint program.
8. Fill the image with black - it should be a solid black square.
9. Save the image.
10. In DXTBmp, load the gp_Signs_Black.bmp file from the Textures folder (solid black).
11. Alpha/Import Alpha Channel. Click OK at the warning, browse to our gp_Signs_Black_ALPHA.bmp file, and click Open.
12. File/Save As/Extended Bitmap
13. Choose DXT1 from the drop down box (NOT DXT1 no alpha!) and click Save, OK to overwrite (after confirming this is the file in the Textures folder).
Now add our new texture to the ADE-GP System.
1. In ADE, Tools/GP Texture Editor.
2. In the drop down box, find our gp_Signs_Black.bmp file, it should have (No Def) after it.
3. Click the No button in the Uniform section.
4. Enter the number 20 in the Pos'n in List section to put our new entry next to the other Sign colors.
5. Click the Update Texture Definition Files button.
6. Click the Close button.
Now you can reload your red letters created above (if you created them), change the texture to gp_Signs_Black, redo the vertices around each letter/number, and you will have black letters instead. Or just use our new black letters instead from the beginning.
Hope this helps,