Why would you want to get rid of anti-aliasing? Any posters printed in TF2's era would have smooth letters. An artist would paint the original (maybe using stencils for lettering), and the press operator would photograph it to be transferred to a printing plate.. there would be no jaggies unless you consider halftone dots to be "jaggies".
So I guess, if anything, the problem is that the text he's using doesn't have an organic enough feel to it. This could probably be remedied in his image editor by rendering the text to a layer and using filters to "humanize" it.
Another thing to keep in mind is that these posters look different in game. By the time they get turned into vtf's and shrunk down as an overlay, they soften up quite a bit.