1.Does he mean he and she are the perfect couple?
2.From the lyrics below " What does worldwide mean?"
Who would have ever knew
That we would ever be more than friends
We're real worldwide, breakin' all the rules
She like a song played again and again
That girl like somethin' off a poster
That girl is a dime they say
That girl is a gun to my holster
She's runnin' through my mind all day, hey
From song : Replay by Iyaz
As we so often say in this forum, words and phrases are often used because of their sound, the rhyme, rhythm and overall effect, rather than their meaning.
Well, guns and holsters do go together and complement each other. That said, it makes more sense if he is the gun and the girl is the holster.