At WordBiLLY.com we've been making custom word signs and one of the items we offer are custom Twitter ID pieces to be hung/placed at the office and/or home. Would this be a problem with Twitter? With the recent talk about Twitter's guidelines, I wanted to ask this. I am aware that asking this is also a risk but at the same time, I wanted to put it out in front of the community.
No, signs with Twitter handles should not be a problem. Twitter is limiting access to their API for retrieving twitter feeds. You're not using any of their resources, so you're fine.