There was this plug-in I had on my 1.6 server called spray id. What it did was it showed you who sprayed their spray on the map when you looked at it, like this:
Which was really useful to find out who was spraying tubgirl everywhere (for example lol), and generally a pretty cool little plugin.
It would be an improvement on the original if only admin's could see the sprayer's ID.
If it helps in anyway the original plugin (and the amx code) can be found
in this thread.