Admittedly I haven't paid a close attention to this tree for a few months but the other day I spotted several of these spots on my pear tree. So what gives?
I'm afraid its Pear Rust, sometimes called European Pear Rust - its one of the gymnangosporangium rusts, and as such, needs two different plant species to complete its life cycle, in this case, Pear trees and Juniper plants. If you have a Juniper in your garden, it might be worth removing it, but usually, this plant is widely planted and if your neighbours have a juniper, then that's not going to work.
Unfortunately, in the UK, there are no effective fungicidal treatments suitable for use on food plants which will control or kill it, so control is usually based around pruning out visible growths on any Juniper plants nearby; Junipers with this infection produce orange cankers or swellings on the stems, with horn like projections in spring if the weather is damp, so pruning those out does reduce the problem.
Rust may be unsightly, but it doesn't usually kill the pear tree - more information here https://www.rhs.org.uk/advice/profile?PID=236