[Mauzen]

Id also like to know people use it. Afaik it wont have any effect, global variables are global and so "public", you cant access filterscript variables even if they are public, and the "host program" wont ever access any public variables of the script. So theres no reason at all why you should make variables public for samp scripts. Maybe the guys who did that just used it as some special symbol in variable naming.
BTW the code snippet from ****** doesnt use public variables, the @ isnt the first symbol of the name, so it is just treated as part of the variable/tag name. The @ just has a meaning when it is the very first symbol.