Actually, both of these gave me a chuckle, I can't think of anything good for the others, but it would be fun to try.
Maybe you can do something with the "Hidden Driveway" sign.
And maybe the Dominator sign can be the stop sign.
Try a few of these: http://www.centurygs.com/images/products/caution2.jpg
Personally I giggled incessantly over 'Watch for Forklifts' when thinking in terms of a good sign for Controllers and having a grav one...
the hard part is that the best signs to use for this has text and graphics, and most sings i could find had text or graphics.
i also think it would be funny to put stalker on a handicap parking sign. 
there needs to be one for blasters plain and simple maybe on a road work ahead sigh saying road damage ahead or something of that nature
[url="http://teenage-kid.deviantart.com/"]My Da page![/url]
Virtue
Ninja-Bee- 50 Ninja/Dark MM
Aqurian Draconum- 50 Archery/Fire Blaster
Korrawi- 50 Super Strength/Invulnerability Tank Plus many others!
Ok, I came up with a few more, let me know what you think:
Dominators
Blasters
and stalkers
I love them. Especially the blaster one!
Awesome love the blaster one my main toon is an archery/fire blaster and im currently rolling a stalkers love them both!
[url="http://teenage-kid.deviantart.com/"]My Da page![/url]
Virtue
Ninja-Bee- 50 Ninja/Dark MM
Aqurian Draconum- 50 Archery/Fire Blaster
Korrawi- 50 Super Strength/Invulnerability Tank Plus many others!
A while ago, I thought up the idea for my current avatar and thought it was funny, so I decided to see if I could do the same for the other archetypes. It didn't work out as well as I would have hoped, but here's a couple more that I came up with:
Brute
Corruptor
I don't think these are quite as appropriate as the Mastermind, but I was wondering if you had any other ideas for something like this.
(and also, if there ends up being one for every AT, or at least every villain AT, if anyone could make it into a slideshow gif, I would be much appreciated)