I consider proper jumpseat etiquette to be a reflection of the individual's professionalism (or lack thereof).

As a captain I definitely prefer any (and all) jumpseaters to introduce themselves and show ID/ offer credentials etc. It is simply good manners, if nothing else. I jumpseated extensively a few years ago and would always make a point of stopping by the cockpit after the flight to say "thank you". Again, it's just good manners.

I find that in general people appreciate good manners. It doesn't cost you anything to say "please" or "thank you". Opening doors for people, pulling chairs back at the table, waiting for the hostess to take the first bite, etc shows appreciation and respect for others. I promise you it is noticed!

To me when you jumpseat off-line, your conduct reflects the entire pilot group at your airline. If you are professional and polite that reflects positively. If you show up with ear buds, tie pulled down, un-ironed uniform shirt and say "I'm your jumpseater" you come across as unprofessional and an ungrateful slob. That's not a very good first impression!