There are online translation services like http://babelfish.altavista.com/ I agree with Tony that you should post them in Portuguese. I'm assuming that you have pictures with the text in Portuguese. It doesn't really matter because the text is inside the picture. However you can type the Portuguese in online and then clean up anything that doesn't quite carry over to be understandable English. The translations rarely come out to be perfect, but the tools do work. Just a suggestion.
Since there aren't usually more than 10 words or so in people signs, they could be in Portuguese, and then you could translate yourself into english in the caption without too much work. Do you think that would work?