He is a professional footballer. Not a group of people who, in general, are known for their intelligence.
He can wear what he wants and I couldn't care less. Other than looking at it and thinking he is a complete dick then it doesn't register.
Mind you, I'd think anyone wearing it was a complete dick as obviously, somewhere along the line when purchasing the said t-shirt he must have gone through one of the following thought processes:
"Hey, I will look really good in this t-shirt with a gun on the front, I'll buy it."
Which is obviously bollocks.
Or, more likely
"Wow, a t-shirt with a gun on the front. I'll buy that and people will see it and recognise that I am street and well into the gangster/hip hop scene."
In which case he is obviously a dick because it is a gun, not a music t-shirt so he must get off on 'gangsta' cock waving and bravado bullshit.
Either way he is a dick, but there are thousands of dicks who think the same and who think that wearing a picture of a gun on their front says something about them. So in the big picture, it's not worth bothering about, other than to shake your head at his reasoning.
PS: I don't mind 50 cents music but anyone who thinks he isn't a bit of a tool, posing with guns all the time, needs to sort themselves out.