It could be a scam...there have been several in the past that operated that way...more than likely it is a Trooper endorsed solicitation. They should be able to provide you with information you can confirm by calling the local Trooper post.
What I dislike is that the Troopers receive a ridiculously low amount of the money from this type of solicitation...something like 10 or 15 percent of your donation actually makes it to the Trooper Association.