A few years back while working on my MA in Linguistics, I saw that there was a lack of availability of fun, linguistics related t-shirts on the market, so I decided to take matters into my own hands. I came up with the following linguistically-inspired mottos for t-shirts (only one of which I had made).
SEMANTICIANS MEAN WELL
SYNTACTICIANS KNOW HOW TO TURN A PHRASE
PHONOLOGISTS RULE THE SOUND WAVES
PHONETICIANS ARE OF SOUND MIND
PRAGMATICIANS KEEP IT IN CONTEXT
MORPHOLOGISTS CAN AFFIX ANYTHING
Because I focused on topics in semantics while working on my degree, I had about 20 or so of the "Semanticians Mean Well" shirts made. I gave them away to friends and family to spread my love of linguistics. I also gave one to Professor Margaret Winters at Wayne State University as she was my thesis advisor and a huge inspiration.
I would love to hear more linguistically-inspired mottos if anyone out there has ideas. Let's give the t-shirt printers some inspiration.