Question: My wife was telling me about a movie or tv shows she saw a long time ago...but can't remember what it was.

A group of people have numbers on their foreheads, which is atypical. They don't know what the numbers are for, but eventually realize that they are the number of days they have left to live. When the countdown reaches 0, something will come for them.

I know this isn't a lot to go on, but it sounded so intriging that I'm very curious. Any ideas?

Answer: 
It's only tangentially related, but Michael J. Fox's 1996 movie [The Frighteners](http://www.imdb.com/title/tt0116365/) features a ghostly serial killer who puts numbers on his targets' heads. Only ghosts (and Michael) can see the numbers.

It's not a close fit to what you describe, but it could be what was being referenced, since you're getting this description second-hand. It's possible your wife got this confused with the Nickleback video Dav referenced in the comments.
I think the movie you are looking for is called, In Time. Time is currency. It stars Justin Timberlake.