Assalamu alaykum wa'rahma-tullahi, wa'barakatahu
greetings little Bro!
i MAY be able to assist you on this!
first of all, DO NOT just say "Salaam Alykum". why, cuz almost anybody knows this phrase. make sure you say AT LEAST "Assalamu Alaykum"; because it's more proper and they MIGHT get the hint. BETTER to say "Assalamu alaykum wa'rahma-tullahi, wa'barakatahu"! cuz now they will have to pause to think "wait, he said that right. maybe he IS a brother!"
try to catch their eye before speaking. if they are looking at you, bring your right hand over your heart and then raise it as a greeting.
if that don't work, simply add "Alhumdulillah, nice to see you today" make sure your hand is over your heart when you say "Alhumdulillah"
and shave the mustache off completely. i don't care if it makes you feel older. learn Seerah, follow Seerah. like once a month, lose it completely. i used to just trim mine, alot-but just a trim, i started eliminating it completely and just shortly afterwards a Sister DID say that it was my face that told her i was a Muslim!!
but seriously, learn Seerah, follow Seerah! the more you know about the Rasoolulah (pbuh), the more you will 1) love him, 2) think like him, 3) behave like him. this will assist you greatly in having folks recognize you.
you're in school right? you have a backpack? get a long shirt or a thobe and keep it in there at home. put it on outside your house!
may Allah(SWT) strengthen you and help your Iman to grow and may HE cause those around you to recognize your attributes as well as your identity!
i have other ideas if your interested.