when I was in school I was given my boyfriend's letters- he lavaliered me and from then on I was allowed to wear his fraternity letters, like say a hat or a shirt with his fraternity's name. I wasn't allowed to wear or have the crest, however. But that is understandable. So basically at my school being given letters is a big deal- it means that he loves you as much as his fraternity- something he has made a life long commitment to.
Rush shirts and dance shirts aren't the same, anyone could wear those, but when I got my FARMHOUSE (His fraternity) hat, I was excited, especially since it was his pledge house, which was a HUGE DEAL!!!
BTW We aren't together now.