There is. It's called a bounty and is explained in the Help Center:
If you’ve asked a good question, edited it with status and progress updates, and still are not receiving answers, you can draw attention to your question by placing a bounty on it.
A bounty is a special reputation award given to answers. It is funded by the personal reputation of the user who offers it, and is non-refundable. If you see a question that has not gotten a satisfactory answer, a bounty may help attract more attention and more answers. Slice off anywhere from +50 to +500 of your own hard-earned reputation, and attach it to any question as a bounty. You do not need to be the asker of the question to offer a bounty on it.
