Well that's hard to tell, especially in comics. Sometimes the energy signatures are commented on as if they are visible, sometimes they are not. For example, Psylocke, when she uses her telepathy, has a purple butterfly appear over her forehead that others have commented on as her signature. Gambit's cards sometimes glow with pink energy and leave a comet tail, while other times they just fly fast and explode with no signature. Depends on the writer, the artist and the medium.
I would assume D&D would be as visible as spellcasting except when specifically called out (IE invisible mage hand). So if the spell calls on a specific visual or audio effect (like knock's loud bang) I would say the psionic version should as well. No more. No less.