The snarkpit search feature is currently out of commission, but Google's is not. I google searched:
site:snarkpit.net "info_overlay"
and it yielded this result:
http://www.snarkpit.net/index.php?s=forums&f=6&t=3127
but it seemed to not help me. What I have is a custom decal texture I want to apply to a slanted surface of a func_rot_button. I would LOOOVE to just use the infodecal entity method, but the decal leaks on to its neighboring brush faces. In hammer it looks great... but compiled, the infodecal doesn't just stay on one face, as I'm sure you know what I'm talking about. (play tf2 and spray your spray on the bottom portion of a wall.... it will often spill onto other faces (as it is designed to do) See picture below.

anyway...it seems info_overlays only apply to the brush face keyvalue specified. This sounds great and all... but I cannot get it to show up in-game when I want it to. If I simply put it on a flat wall... its fine. I can resize it etc in the 3D window... and it still shows up. however, when I apply it to the 45 degree angle button, it does not show up in game. I choose my texture, choose the overlay tool, apply it, resize it, looks fine in hammer, compile it fastvis fastrad, no joy. buildcubemaps.... just in case... still nothin. The texture does not show up.
again... the infodecal shows up o nthe slanted button edge.... but not the info_overlay.
NOTE: I did some various testing before I posted. I applied the overlay texture to various elements and compiled. HEre are the results.
I applied the decal overlay to:
-world brushes: works (shows up in hammer/hl2e2 properly)
-func_movelinear: does not work (shows up in hammer / does NOT show up in game)
-func_detail: works/works
-func_door: looks good in hammer / doesn't work in game
-func_rot_button: looks good in hammer / doesn't work in game
Final thought: info_overlays work on static world brushes and static brush entities, but does NOT work on dynamic/non static brush based entities. It does not specify this in the VDC as seen
here and
here. Did they forget to mention this, or am I not doing something right within the overlay's settings or whatever...
My last resort is making an entirely new texture with the hand print built into the texture to imitate a decal. If it is the only way to do it and make it look good at the same time...