Signatures that can be erased easily aren't a great fit for a legally binding document.

For more information, you can check whether the ink complies with DIN ISO 12757-2 and/or read up on "Dokumentenechtheit" [1]

[1] https://de.wikipedia.org/wiki/Dokumentenechtheit (It hasn't been translated to other languages yet.)

Apparently my every signature ever has been ISO compliant without me even knowing about that norm.