i wear rings on my 'wedding ring finger' even though im single. i do it cuz i like wearing rings! and so do all my single friends. and i wear a gold ring on right finger all the time
I don't wear any rings only because mujhe jewelry se uljhan hoti hai ( i know i know a dream come true ;P ) but nothing wrong in approaching a girl and if shes married, and you are polite, she may be flattered but as lon a you aren't "HOW YOU DOING?" every feminine creature with legs, you should be okay.
Isn't the wedding ring more of a western concept? Desis/Muslims may or may not adapt it. I know many who couldn't care less about this.
I am more interested in knowing western concept because its the western women who confuse me the most. For Muslims and other easternized women it is easy to tell if they are single or not.