I don't think his choice of and number of pens used is what is worrying.
What is worrying is watching a 70yr old man struggle to read something my 7 yr can without even trying. Try to parse what he leaves as a signature with the letters that actually comprise his name. Listen to him try to say simple phrases and sentences, how he turns it into a multi-point description, replete with continuous pauses, stutters, non sequitur, then repeats bits and pieces in whatever order he wants giving the audience the impression he's either crazy or has the attention span of some kind of insect. That's not even touching on the vast amount of ignorance he displays on policy.
Like the cast of SNL found out when Dump hosted, he can't really read like the rest of us. Punctuation and proper grammar make him confused, which is one of the reasons he doesn't get jokes. Whatever mental illness he seems to be suffering from sure ain't helping.