Does anyone use "SN" in email signatures while a student?

Are you referring to your work e-mail? If so, including your degree and EMT certification might be appropriate. However, including SN is not appropriate and should not be included.

I wouldn't.

Given student nurse is not your role in the workplace setting I would stick to your current role/certifications in your work e-mail. It is appropriate to include the student nurse (though not EMT / work role) in your school e-mail.

SN is a role, not really a certification or a position. I would not include it. If it was a school email, maybe.

You should not include BS unless you have that degree. If you have that degree, include it.

Only when contacting my professors, nothing for outside of school.

I personally wouldn't use it either, though in the past I thought about using it in email exchanges with my professors. If you used SN, I don't think anyone will be impressed; at worst, I could see people thinking you're an up-nosed nursing student using a made up title to distinguish yourself.

I'd just wait until you passed the NCLEX - then you can use your degree, licenses, and professional nursing certifications all you like!

SN is ONLY for school/clinical experiences.

We were always told to use the designation 'student nurse" because SN could be mistaken for staff nurse

My school uses the abbreviation "NS#" with # being the school year we're in. I'm actually doing my clinicals for this quarter in a different department at my workplace, and as such sometimes I have to use my work email for school purposes, so I've added NS4 to my e-mail signature there.