Immature pears do have thorns, but lose them as they mature.* I suspect your pears aren't grafted trees as most are sold grafted with tops that have matured past the thorn stage.
Here's a similar question I answered on a UK arborists forum 2 years ago.
The problem is often that any fruit from a tree that isn't grafted could be anything and the fruits are often inedible.* Do a google with:
pear + thorns and you'll get some interesting info.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.