Hi! just want to ask about helmet holders/locks?

Pretty new in biking and sometimes have difficulty in carrying around my helmet when I got to the mall for a short while...or watch a movie etc...

wondering if there are" off the counter " helmet locks for a sportster... I plan to park somewhere safe (eg.near security guards, place where I can still see the bike from a distance etc. )but at least I can leave it with my bike for a short while...

if ever there are.. where and how much? Its installed somewhere below the seat?

Thanks!