Problem with wet signatures

We use the option of signing documents by hand (so called wet signature by downloading, printing, signing and then uploading). It has often happened that customers forget to wet sign the downloaded document by hand and instead upload it without a signature. Adobe Sign allows this step.

Is there a way to prevent (or at least get a warning for the user) when a non signed document is uploaded?

There has to be a security mechanism, otherwise the entire legal validity of such signature processes would be gone.

I am grateful for every suggestion.

Andreas Hofmeister