I often use "드림" at the end of the mail with my name when emailing to my boss or somebody who I think need to show respect, mostly strangers or persons than older than me. "씀" is used to persons who you know and are close, often the same age as you or younger than you, as chin.billy.leung mentioned above, it is often used in a short note than a letter.:) \^o^/

유나 씀 - informal 유나가 썼다 유나 드림 or 유나 올림 - formal 유나가 드린다 or 유나가 올린다 씀, 드림, 올림 is used only in a mail.

쓰다. to write 드리다 to give 올리다 to submit, to lift up to they are all transformed into noun. this style is very common in notes and signs. Koreans love nouns