Does using 'pen' as a verb unambiguously mean that what is written was written with a pen?
I am rewriting an employee handbook. I have a goal of making the handbook more understandable. In some cases this means I have to put more ideas than what the previous handbook has, because the previous handbook was ambiguous (or sometimes it didn't even explain something that we have treated as a rule anyway).
However, putting new ideas means putting more words. Putting more words can slowly deteriorate understanding (people can only pay attention for so long).
In an effort to be more concise, I considered changing the sentence "Please sign your name legibly and in pen" to "Please legibly pen your signature."
In retrospect, I realize that this probably won't make things much more understandable, but I still wonder: If I say someone should pen their signature, does that unambiguously mean that they should use a pen?
I've provided definitions for "pen" as a verb (which YOU should have provided! That's OK, you'll know for next time).
If you're asking whether the verb "to pen" can include using a pencil, then the answer is clearly yes, as shown by the dictionary definitions below.
To write or compose: penned a letter.
American Heritage Dictionary(tr) to write or compose
Collins English DictionaryWrite or compose.
Oxford Living Dictionarieswrite, indite * pen a letter
Merriam-Webster Dictionary
14. to write with or as with a pen; put down in writing: to pen an essay.
15. to draw with or as with a pen: to pen a sketch.
dictionary.com
7. to write or draw with or as if with a pen: to pen an essay.
Random House Kernerman Webster's College Dictionary
So the only definitions here that explicitly mention using a pen in the verb definition of "pen" are the last two. And they don't require a pen, they're written in terms of "with or as if with a pen" or "with or as with a pen".
Merriam-Webster defines the verb as to "write". And I don't think it's controversial that you can write your name using a pencil.
I personally wouldn't use your phrasing of "pen your signature". Have you ever gone to fill out a form before stopping yourself and wondering "I wonder if both pen and pencil are acceptable." The verb "pen" to specifically mean using an actual pen most likely IS ambiguous. Take the following examples:
"Previously unpublished letters penned by struggle hero, Nelson Mandela, primarily during his 18-year imprisonment..."
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Can we tell whether he used a pencil/pen/crayon/chalk/smartphone stylus/finger painting? OK, so some of those are crazy, but pencil or pen are both likely possibilities.
The song was penned in George’s family home after an average Sunday dinner and became an iconic Christmas song that made the playlist we all listen to every Christmas on a loop.
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This is in reference to a song. Assuming these were lyrics and not music notes, do we know whether a pen was used? No.
If you hand someone a form and a pen and say "pen your name" or pen something else, then it's more obvious you want them to use a pen, more specifically the pen you gave them. But it's better to avoid this phrase in my opinion. "To pen" is often used in place of the more ordinary "write" maybe in an attempt to sound more creative because "write" is seen as common and prosaic. Also "To pen your signature", I'm not sure about that. Wouldn't you rather be more clear and say something like "Please sign your name" or "Please write/provide your signature."?
The alternative in your question:
"Please sign your name legibly and in pen."
Leaving apart the fact that, as jlovegren pointed out, signatures are often illegible (intentionally or unintentionally), the last part of the request specifically states your desire that they write their name/signature in pen.
So yes, it is very often ambiguous.