Thank you for getting started. I have a few comments.
In #79, the symbol looks like a droplet of something, maybe a drop of water. I would like to avoid droplets. And the top of the T is too wide. I like that you tried something a little different, but I don't think it fits. But I see a negative white T within the symbol. That could be interesting if you somehow turned that into the T in Topo, but I don't know if that would work.
In both #79 and #78, you used orange, which I'm not too sure about.