Same for the 4x4s I get. I did a couple of hundred of them for a reunion.
The 4x4s usually have 3 sides that are unglazed with one side where the glaze wraps over half or more of the side thickness. None of the sides have tile setting tabs.
I color the sides with an oil paint Sharpie - either black or color matching the coloring I applied to the engrave. Takes just a few moments to slide a wide/chisel tipped one along the edge.
Take a look on Facebook for some βFreeβ groups in your area. My wife is on our local one and when I started doing the tiles, she posted to see if anyone had any. Within a couple of days I received a few hundred tiles of all sorts of shapes and sizes, all for free. Some were just regular ceramic tiles but I also got quite a few marble tiles from that request as well. Most of the tiles came from people that had done remodels in their homes and had leftovers that they just wanted gone. It surprises me what my wife finds in those free groups some days!
and @jason.fuller0 I just got back from the local Restore. That is a dangerous place. I ended up with a bunch of tiles and some wood clamps!
Thank you for the tip.