I have a few Spyderco lockbacks that have very slight vertical play, but only noticeable when applying heavy cutting pressure against the edge. I have never felt play in one by shaking it up and down in the air; somehow it sounds like a bit of a problem. Or perhaps its noticeable due to Police's heavier blade?
Hopefully Sal will be able to reply and we will find out for sure if your type of play is within normal spec.
(by the way, when inspecting knives before buying, including some SS-handled ones, one of my tests is putting some pressure on the blade in a way that duplicates the pressure the blade might receive if cutting heavy; that is, I'm not trying to defeat the lock, but pushing in the opposite direction. I occasionally will feel play in certain ones, so I usually ask to see about 3 of a model I plan to buy and inspect them for play, also if, when in closed position, the tip is down far enough into the handle but not too far down). But still have never noticed feeling play that would be noticeable when shaking.