-v true -a produces invisible signature when invoked via CLI on Windows — is an additional flag required?

[MaWaNo]

Steps to Reproduce

call

"C:\Program Files (x86)\PDF-Over\PDF-Over.exe" -i "<some.pdf>" -o "<output.pdf>" -b MOBILE -a -s -v true -e "<any-small.png>"

Expected Behavior

Signing works fine. However, there should be a visible signature in the signed pdf.
Are there some other options requiered? I also tried with -v "true", but no difference.