What is the best marker for writing on my phone?

I'm going to a concert and I want the band members to sign the back of my phone. I have an iPhone 4, which has a glossy, black surface on the back. I need a marker that is metallic or brightly colored and will show up. What kind of marker can do this? It can't be the kind that rubs off immediately either. It needs to stay long enough for me to get it home. Then I need to put some kind of sealer thing on it. Can anyone recommend a marker and sealer that will work for this? Thanks :)