How do I determine whether it is signed with highS or not ?
Step 3: check, whether the S value is below the curve order
The is an easy rule-of-thumb to spot high-S signatures. For example, the following sig is high-S
3046022100aea3c7faf22df9ecf795ddb470d000bb2345679363fde6c24df4ab9c6922ff5d022100ae2ff77a2cd10794f166cbb7782316d6ceb74fc22c2188a22c52f6f1847401fa01
If the highlighted hex "022100" appears in the
middle of the sig, then it is high-S. Compare with the low-S equivalent:
3045022100aea3c7faf22df9ecf795ddb470d000bb2345679363fde6c24df4ab9c6922ff5d022051d00885d32ef86b0e99344887dce927ebf78d2483271799937f679b4bc23f4701
The low-S has "0220" (highlighted) or something else.