Didn't intend to imply that they didn't exist (just that I had never seen any myself), but I'm just going to show myself out before I make myself look any dumber.
Don't feel bad--I found UT roads in St. Louis County only because the plans for the SP 8821-353 sign replacement furnished a cheat sheet. MnDOT signing contracts with control sections of 88XX tend to be districtwide jobs, but this one focuses on US 53 in St. Louis and Koochiching Counties. In many cases, perhaps most, UT roads will be signed far more conspicuously from US 53 than they are now.
Here's an example:

Google Maps not only
fails to show Jacobs Road as UT 8146; it also misleadingly labels it as CR 519. StreetView imagery (the latest of which dates from November 2015) shows a
UT 8146 shield on Jacobs Road itself but no existing signing on US 53 referencing a UT route.
I don't know the current status of construction on SP 8821-353.