Generally we don't want watermarks on anything unless they're on the source files (like the onlyfans watermarks). Adding a watermark that advertises an outside site or group (like a teIegram link) is expressly forbidden.
If you're creating content it's fine to add your name to it, like if you're posting artwork, personal pictures, collages, deepfake stuff, etc. Just make sure it's getting posted in the right areas, since most regular threads don't allow edited material.
Adding a watermark on top of pictures you get from Onlyfans and such is discouraged.