How to verify a trusted Issuer in U-Prove
For any credentials scheme, trust is defined out of the scheme. It might be your employer or your government.

Please note there is no clear separation whether signature is coming from Issuer or Prover. Signature on token public key $h$ is verified with Issuer public key (Figure 4) as a proof of equality of two logarithms. However, it is created by running a blind signature protocol running both by Issuer and User (Figure 8). There is no chance to create this signature without Issuer private key $y_0$.

Please consider to double-check Issuer parameters generation (section 2.3.1): once on scheme setup.