Searching for question marks in VIM

[thesheep]

How do I search for a string starting with a '?' in VIM (I want to replace it with £)?

I've tried:

:% s/?/£/g and also :% s/\?/£/g to try and escape the special meaning of '?' but neither of these two work...

[thesheep]

Nobody?...

[coopster]

Looks correct to me except for the space between the range and the search pattern, get rid of the space:

:%s/?/£/g

[thesheep]

Hi, actually it seems that the space there doesn't make any difference.

But I think I'm figuring out what's going on. I've got a file written on Windows, with a bunch of pound signs £ in it. When I look at it in VIM on OSX, they show up as ?
But now I'm thinking that these are not actually question marks, they're the windows character code for the pound sign, which is probably what I need to search and replace.

Now I just need to find out how to do that...