Have you seen this thread?
"[STOCK] Custom kill message icons"
https://forums.alliedmods.net/showthread.php?t=330116
edit: You probably have, since it looks like you are trying to do the same as them
I will try to make it work myself and get back to you.
edit2: I can't even manage to get the fall damage one to work. I wish you luck, sorry to be of no help.