Email Signatures - Hello, This Is Me

The email signature is the who you are, where your from and what you do at the end of your email.
It's your advert, use it to advertise yourself.

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Your emails signature should contain all your relevant details, what these are will depend on who your audience is.

If it's a business contact then obviously it should be fairly formal and contain details of you, your role/responsibilities and business contact details including your business address.

The idea here is to communicate the image and details of who you are in a professional business like manner, an extension of your business self. Unless you're a creative person then it's best to stay away from smart references or quotes as a tag line, even if you are it's probably best to leave them out.

The signature has got to help portray you in the way you would wish to portray yourself in person in a business setting. If you're adding a signature to your personal emails then it's fine to include items that show your personality or interests like famous movie quotes or references, lines from poems etc. You will most likely want to leave out most of the details relating to your business as most personal contacts will either know them already or be more likely to ask you in person.
The main thing to remember is that the purpose of the email signature is to communicate who you are and how people can get in touch with you in a manner that fits in with the relationship you have with them. The details needs to be relevant to the recipient of the email.
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But not always The problem with email signatures is they can take up a fair chunk of space, space that doesn't need to be filled all the time.
If you're replying to an email and you started the email conversation then you really don't need to repeat your full email signature on every message.
Over use of your full signature will just degrade the effectiveness of it as people will automatically mentally filter it out after a while.

Consider leaving it out all together or have a shorter version for replies that may include your name only or maybe a main contact number as well.
Again remember that the details send have to be relevant to the recipient of the email. An effective email signature is one that gets the relevant points across without over doing it.