This is funny. I'll give Evan Mathis that. However, at the same time I don't think it was a very wise thing to do. It doesn't matter if he actually did or not the message that he is trying to get across by looking like he is urinating on an IRS sign is pretty clear (totally makes me think of those Calvin decals).
Hopefully for his sake the IRS is not feeling vindictive. If they are I'm sure the veteran guard preparing for his ninth NFL season can afford a good accountant.