Half-Life wall writing

Off-Topic
,
1

I was just playing the SP and I saw some blueish lines on some walls. When I looked closely I was able to make up something.
This is the original image.
http://img148.imageshack.us/img148/8773/c1a20000.jpg

And here’s what I think says there.
http://img148.imageshack.us/img148/3280/themesage.jpg

Is that the texture name?

2

I think it says R-8 13b

3

Yep, I’ve noticed that before.

4

Why would Vavle put that on the walls anyway? Is it a easter egg?