They won't force you to use a particular pen, but they must take reasonable precautions that you are using permanent ink. Notaries must protect their seal, and

They won't force you to use a particular pen, but they must take reasonable precautions that you are using permanent ink. Notaries must protect their seal, and don't want you to sign as Joe Blow, get the seal, then wash the signature off at home and re-sign as Donald Trump. Washing a signature is trivial with many FP inks, so most notaries don't want you to use them- it's too much trouble to verify which inks are safe, and much easier to ask you to use a ballpoint. Those that do allow it are risking losing their license (admittedly a small risk) if they get caught up in fraudulent signatures. Notaries that allow FP inks are either just accepting the risk because they don't want to be a dick or they are not aware that by using FP ink you might as well be signing in pencil.