I don’t know. I just tried looking it up. There is a way in the Marcomannic runes for writing the R that I guess you could say resembles how Tyr did it. But it looks more like he’s using a way to write the T from the Dalecarlian runes. In fact if Dunlap is trying to make it look runic, did he have the Marcomannic and Dalecarlian runes both in mind. Both the T and Y look like their from one of the ways to write them in the Dalecarlian runes being written by someone with bad handwritting (like me).
But you’re probably right, more meant to suggest a level of illiteracy.