I prefer to use my own pens whenever I can.
I always had a supply of pens available to my clients for filling out and signing documents, and kept my personal pens separate. My associates did the same thing.
I don't see anything odd about it.
ETA: Gross as it seems, fecal matter is found on just about every surface we touch.
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"The truth is like a lion. You don't have to defend it. Let it loose. It will defend itself."
- Augustine
Be Vigilent