I recently presented a poster of my preliminary PhD research at a conference, and placed both my name and supervisor's name in the author position. I thought this was normal academic etiquette, but when I looked at every other PhD student's poster/presentation, they had either only put their own name, or their own name plus the name of their collaborator (if they did a joint project).

Because of this, I kept being asked 1) if I was presenting my supervisor's work in her absence, or 2) if I was my supervisor (because her name was more centrally aligned than mine, and therefore more obvious). Just in case it's relevant, my supervisor could not attend the conference, so I presented my poster alone.

Is it normal to only credit yourself on posters/presentations when you're presenting your PhD work?

What is the field?

I am in engineering and I put all my supervisors on my posters, usually they haven't seen the poster. I agree it would be a bit rude to leave them off but I bet it depends on the field.

If I remember correctly I put my own name either in larger font or I underlined it to indicate this was my research. My supervisor's name was on everything I did as reference.