Custom Fields Customization

I’ve started using custom fields in my blog in order to display music, plugs, and so on easier. However, the process of implementing them does not make updating any less stressful.

Here’s the issue: I am using images to indicate what exactly the visitor is reading (a plug for plugs, a speaker for music). Apparently I can’t make use of them as emotes, (:phn: and :plg:), so I use an img tag. Because of this, I have <img>:. I do not want a colon. So! Does anyone know how to make emoticons work in custom fields, or where do I find the code in which the custom fields layout is defined, so I can remove the colon?