How can I etch titanium without hydrofluoric acid?

Perhaps with a laser, or using a CNC machining tool? Neither option is a backyard operation, nor cheap. With laser engraving you can achieve colors by modulating the settings on the laser, which is nifty.

This may be helpful although it may generate some HF in situ Phosphoric acid and sodium fluoride: a novel etching combination on titanium https://pubmed.ncbi.nlm.nih.gov/24704898/