Cycling on pavements is illegal unless signed otherwise - so it is the absence of any signs allowing cycling that is the key. 

So the point at which the pavement heading out from Lascaster ceases to be shared use is actually at the junction before the dismount sign. You can see shared use signs and give way markings on the pavement heading west, but not east. And you can see cycleway markings in each direction at all the junctions it crosses till it reaches the other end at Lansil Way.

I guess the Dismount Sign in this case is just a reminder to those who inadvertently continue to ride illegally on the pavement. It has no legal meaning and are used (some would say abused) for a wide range of different purposes. 
