I have several t-shirts that suggest that I reject the idea of a deity. I wear them selectively; I wouldn't wear my Flying Spaghetti Monster (FSM) shirt to a funeral, for instance.
Mostly, the shirts would only be offensive if the person already knew what they represented. For the most part, the shirts would go unnoticed or passed off as just another novelty tee.
If someone were to ask about the shirt, I would have no issues discussing it.
If someone expressed that they were offended by my shirt, I would suggest that they stop looking at it.

Where does this notion come from that suggests that, because one is athiest or agnostic, that one is therefore rational? And the corollary being that one who is theist is not rational? Human beings are not only prone to irrationality, but we are predictably irrational. Declaring ownership of rationality, and labelling those outside your 'camp' as irrational, serves only to divide on top of being factually incorrect.

A person can arrive at the belief in a god through wholly irrational means in the same way that a person can arrive at the belief that there are no gods through wholly irrational means. In other words, I know and have met atheists who have arrived at atheism irrationally.

This whole argument that, because I'm an atheist, I am therefore a rational thinker, is ludicrous at best, and divisive and perhaps dangerous at worst. At the very least, it is not a banner I will rally under, and will do my utmost to encourage others to avoid.

I don't own any clothing that would suggest any particular (non)spiritual leanings, but I do relish a little shock value from time to time. One Halloween, I went on a club run through downtown Baltimore dressed as a giant penis. After that, I suspect a t-shirt or jewelry indicating agnosticism could be considered tame.

My view is not in the list of answers. I don't make a point of my Atheism much and only have a couple "Atheistic shirts" in my collection. All 3 of my vehicles sport decals that promote Science, Evolution, and Atheism (I posted a photo of my car's rear window about a couple weeks back). I don't have to tell many people anyway, I have freely discussed my Atheism pretty much since I moved to Bible Belt semi-rural Georgia. All my coworkers, Judges & many Officers (my job interfaces with them), local Politicians, City/County/State/ Federal Officials, those that I regulate, various merchants and restaurant owners, a reasonable portion of the general population, and pretty much anyone who brings up the topic.

I brought myself a bracelet some years ago and then collected various religious symbols to put on it like a charm bracelet; it had a buddha, a celtic cross, a pentacle and that's as far as I'd got when I started wearing it. A friend got really upset by it, it was quite bizarre from my point of view, and so I stopped wearing it and gathering icons.

I think being in-your-face with one's beliefs, regardless of what they are, is unwise. Too often rude and a sign of insecurity.

Don't talk about what you are, be it. The actions will speak loudly.

As a rule I do not wear anything with slogans, I even try to avoid logo clothing.

I just wear what I want and my beliefs are evident with those I talk to. Plus I’m not a fan of wearing t-shirts.

I don’t wear clothing identifying me as anything but perhaps, male. I find clothing with sentences on them as tacky, but that’s just me.

I find no need to advertise the way my mind works. People are welcome to figure that out the normal way.

I legitimately don't know any kind of clothing that would identify me as a "rational thinker." Are you talking about shirts that say "Atheist" or something similar or are you referring to specific clothing styles/fashions?