A friend of mine told me that the Spanish PRO's use sprinting for signs in almost every training ride that they do. It is probably a great way to simulate the racing feel when out training. Think about it, you're busting a gut, it's four hours into your ride and then whoosh suddenly one of the riders in your small peloton flashes past in an attempt to be first to the sign.
I was reading Michael Barry (Jnr) post on Velonews today and to quote him "As we neared Girona we upped the speed, riding in a smooth paceline, with a sprint for a town sign that is as nearly hotly contested as a true finish line." If you have never read Michael's posts, well shame on you. As a true thinking mans rider (and a real tough guy on the bike) his posts always open a window into the professional side of the sport.
To read it in full go to: http://www.velonews.com/article/77005/michael-barry-s-diary---the-passing-kilometers