I can't get around using individual labels in each set of cells. Some areas near the edges of my heat mat are cooler, so I end up shuffling the cell packs every which direction like a Rubiks Cube so they can take their turn in the center of the tray. I did make a chart using Feldon's nice templates for my peppers, but it's not going to be of much use after I start shuffling the cells.
I make my own labels from cut-up gallon milk jugs, the white plastic purchased ones are all too long. I want them short enough so they stick up less than an inch above the soil line. The clear domes fit better, and less chance of the markers being knocked out by playful cats or clumsy people. I cut them in long triangle shapes, so there is enough room to write on the top edge, they don't have to be perfect. The base of the milk jug makes a nice little tray to store them.
My pepper trays are currently using all the heat mat space. I might not use the heat mat on my tomatoes, but even so I will have the same shuffling problem once they start sprouting. I rotate the outside cells inward so the outer rows of seedlings don't always lean toward the lights, in no particular order, it depends on which sprout first, or which look more spindly.