I have no idea where I saw this and I can't remember anything useful  about the fic except that Sam had his visions but when he tried to draw them out so that they could use the information, it didn't work because Sam can't draw for crap. Dean, however, can draw and somehow he sees the visions so they do it that way. I think it was a crossover with either SGC/SGA or Criminal Minds, because I remember very clearly a scene where Sam has a vision and Dean starts drawing and the crossover character asks him what he's doing and Dean says, I'm drawing the vision out , and the other person says, I thought Sam was the one who saw things. Dean answers, yeah, but Sam can't draw, and the other person's all, okayyy...

That's all I got, sorry.

Found! In comments.