Signature blocks are the pieces of boilerplate text that are added to the end of every email that you send. Some are very small e.g. “cheers, Rick” and some, like corporate ones, are very big.
I consider it important that they contain a certain minimum of information; the reader needs to know who you are. First, for technical reasons, every signature block should begin with a line that contains two hyphens and a space "-- "
at the start and nothing else. This is required by the email standard and allows client software to know when the content ends and the signature block starts. Many products take advantage of this and, for instance, display the signature in different colour.
The second essential item is your name. If you use multiple blocks and select each one according to the type of email, then this can be just your nickname or your full name and formal title according to circumstances, but if you use one block for everything then make sure that it is sufficient to pick you out from the crowd.
Include your email address. I know that there is a return address in the headers but in some circumstances, e.g. if the mail is forwarded, this can get stripped off.
Finally make sure that the block is appended to all mail—original notes, replies and forwards.
Putting large graphics and logos into signatures is considered bad form but other contact details can be very useful. I think I am unusual but I have always included my full address, telephone number, email address and web site URL in every email I send. There used to be a netiquette rule that 4 lines were the maximum but you can go over that if it is informative, just don’t overdo it.
The requirements for company emails are different and the (UK) regulations have just changed. You are now required to show the company name, registration number, place of registration and registered office address, also your VAT number if you have one. It is also recommended to include membership of any professional or trade association. Most companies are telling their employees to include this information on every email, internal or external, whether or not it is a formal communication, just in case they should be interpreted as such and leak to the outside.
On business emails there are often two other wordy blocks of legalese. The confidentially clause which tells you not to read the message if it wasn’t intended for you; a bit late that one as they are almost always after the content so you have just read it. Even so they are considered worthwhile as they should serve as a brake to forwarding them on to other people. If you really want to keep your messages confidential, encrypt them.
The other is the disclaimer clause which says that you can’t rely on or trust anything you have just read; This is a complete waste of time as you wouldn’t have sent if if you didn’t mean it (I hope). They are also legally ineffective. If you really want your messages to be validated, then digitally sign them.