If the signs aren't correct how can a search on them be valid?
The search is still valid the majority of the time. Nothing is perfect.
Why can't their be a question "show your sign or not?"
Why not just get rid of it all together.
.... But POF calculates it so it is correct?
POF based it on what the user enters and many do not enter actual birthdays to the exact day.
Some will fudge by a few years and some will fudge by a few days.
Some that fudge by a few days, do so as they believe it is not a smart thing to do (myself included), entering your actual birthday for security reasons, as birthdays are key pieces of information when attempting to steal ones identity.
I've met too many guys with their sign incorrect on their profile!
If it is a big issue for you, then I would suggest just asking them in an email if the sign that shows on their profile is the right one.
Same thing with age. We should enter our age and POF calclates it so people can't lie, unless they do it upfront for DOB, and it adjusts when our birthday passes?
How does that stop people from lying or not putting in exact date?