Sending a *digitally signed* email to prospective employer/supervisor I have been digitally signing (and encrypting, whenever possible) my official emails for sometime. While I am not extremely paranoid (but serious, certainly) about cryptographic security, I also think signing the email is a signature [pun intended] that I take such aspects seriously. On a like-minded recipient, this could therefore make a good impression. 

On the other hand, if seeing the 


  -----BEGIN PGP SIGNED MESSAGE-----
  
  Hash: SHA1


header has a high likelihood of annoying or confusing the person (to the point of them simply deleting my email), then I certainly do not mind sending an unsigned message. 

I recently started applying for jobs (in the area of quantum information/communication to be precise) and was wondering if I should, in my first email contact with a potential employer or (postdoc) supervisor, also sign that email?
I cannot imagine anyone being too put off by the digital signature, although I would probably go with a detached signature.

I think if you are going to digitally sign your emails, you may want to make sure you understand what you are doing. This would definitely be the type of thing I might bring up as a "safe" small talk topic during a campus visit. Often the small talk conversations can influence a decision in a tight job search since the search committee is not only looking for someone who can teach the required classes and do great research, but also someone they want to work with.