I got tired of running down to the garden store for new plant tags. It was adding up.
So I grabbed an empty quart yogurt container, cut off the bottom and the rim around the top, and sliced it. The drawback is that they're one-season tags: have to use permanent marker. The good news: free!
Also note the start pots on the left: an old roll for Christmas paper, cut into 3" segments, the bottom split into 4 segments, folded under and overlapped.
I found the newsprint technique later, and like it better, but I needed some small ones for this tray. And really, it seems to work. Toilet paper rolls work, too, but they're pretty small.