I found “Mac. Blesa” on a fire extinguisher near the start of the game.
Don’t worry. I’m not playing on an 800x600 game display. I made steam crop the image down low.
Mac most likely stands for Mack.
It would then be Mack Blesa.
Mack Blesa is an anagram for Black Mesa.
At the bm_c1a0a, when the guard has computer problems, the scientist there suggested pressing Control Alt and Delete.