Just a simple 1"x3" keychain tag. You can print a label to stick onto it, or edit the .stl directly to add your own text onto the file. The OnShape link is here.

I made these specifically to label benchies I've been printing as a palette of color samples in different materials - those in the photos are scaled down to be a more appropriate size. A paper clip shaped with a pair of needle nose pliers is great for attaching them.

I've had the most luck printing these on one of the skinny sides, and printed them in PLA in a batch of several at a time.