Alrighty, so my suggestions are for the forums/TF2 servers (might work on CS:GO, but I'm not too familiar with CS:GO's plugins and whatnot)
Custom models. There are plugins that allow you to change your player model/projectile models. Custom player models would be a cool way to show that you're supporting the servers, especially since you'd be the only Captain Falcon walking around.
The bad side is, it's more stuff for people to download. We'd just have to keep 'em under a certain filesize.
The second suggestion is Custom sounds. Some servers have plugins that let certain people play custom sounds over the entire server. Or you could use the sm_play command (which is currently locked to Admin, I think), but uses the built in TF2 sounds (and Gabe's famous "Welcome to Team Fortress 2" speech). I think custom sounds can be played with sm_play, but I haven't played with it enough.
Since sm_play requires the user to also know the directory of the sound, I figure it wouldn't be too hard for me to write a quick menu for Sourcemod to easily find and use the sounds. If it's approved.
I also don't know if it's already a thing, but a neato "Sponsor" tag in game would be cool. I know TF2 is kinda limited in what attributes text can have, but a customizable tag with various colors/effects would be nice. Whatever's possible
As for forum ideas, perhaps we could add some kind of effects for names and text. I know I've suggested the stupid Runescape-esque chat effects for Shoutbox, but perhaps that could also be expanded to also include the entire forums? Nothing too eye-gougingly annoying of course.
Welp, those are my awful ideas for now.