Instead of manually writing your name and contact information at the bottom of each email you send, why not create a personal signature? Windows Live Mail 2012 / 2011 / 2010 supports multiple email signatures, and let you assign different signature to different email accounts: no more mistakes including the wrong signature with a particular message! You can even switch signature on-the-fly, in the new email compose window. If you are composing a plain-text email, your rich-text-formatted signature will automatically be converted to plain text (only new line characters and spaces/tabs will be preserved).
Tip: don't forget to consider changing default font to make your signature and the text in your email body match, or at least be complementary. This kind of consistency definitely helps make your messages feel more professional.
To access your email settings, click on the "Windows Live Mail
" button in the top left corner, and go to Options > Mail (the equivalent keyboard shortcut is Alt+F,O,M). 
Click on the Signatures tab: all settings are disabled until you've added at least one signature. Do so by clicking on the "New" button: 
This automatically creates a new one called "Signature #1
", and sets it as the default signature. For a more meaningful label, click Rename: type a name and hit Enter.
To add a text-only signature block (no formatting) that uses the same font as your email, click in the "Text" box under Edit Signature, and type one piece of information per line; new line characters are preserved.
Links in your plain text signature aren't automatically converted to clickable "hyperlinks" on your end: they may become clickable URLs for your recipients, depending on the email client they are using. To force Windows Live Mail to convert your URL into a clickable link, make sure that it starts with either "www." or "http://". If it does, place your cursor at the end (in the email, not the signature box), and type a space to do the trick! 
Note: your signature should include at least your first and last name, plus job title; ideally, also list your contact phone number / fax, and company website. Since emails are often shared on paper (no guarantee that the email headers will be printed), also including your email address is a good idea.
Microsoft doesn't support rich text format (RTF) signatures for Windows Live Mail, but you'll be get any formatting you want with a standard HTML code (the signature generator will help you with that setup).
By default, Windows Live Mail won't automatically append signature blocks to your emails: with that setting, you need to manually pick a signature whenever you want one: in the Ribbon's Insert tab, click on the Signature button and choose the one you want to use.
But you can change that behavior in the program's options: to automatically insert a signature to all new email messages you compose, check the Add signatures to all outgoing messages checkbox. If you want to include your signature in all mail you send (vs. new messages only), uncheck the Don't add signatures to Replies and Forwards checkbox: 
Tip: the keyboard shortcut to show the signature dropdown (in a new email window) is Alt+i to select the Insert tab, and then the letters i and s.
If you have more than one signature, select the one you want to assign to a particular account and click on the Advanced button: all email accounts currently setup in Windows Live Mail will be listed in the "Advanced Signature Settings" dialog. 
Check the checkbox next to each email account for which you want to use the selected signature (its name is displayed in the description). Click OK to save.
Tip: accounts without a dedicated signature will automatically use the default signature. If you want those accounts not to use any signature, just create a blank one (no text, just a space character) and set it as the default.
To set a signature as the default for all accounts (this doesn't affect email accounts which have a dedicated signature - see above), click on the signature to select it, and click Set as default (that button is disabled when the current default is already selected). 
Click to select the signature: click on the Remove button to delete it. To just change its name, click on Rename, type a new name, and hit Enter. Note that your signatures are displayed in alphabetical order only in this listing, while you can use numbers in front of the name to sort them by order of "frequently used", it will unfortunately not affect their order for the Signature dropdown in the Ribbon (listed from first to last created). 
To modify a signature later on, don't delete it: just edit the text and click OK to save.
Caveat: you won't get a final confirmation before a signature is deleted, but you can "undelete" the signature by clicking on the Cancel button (doing so discards all settings changed since you last opened the Options dialog).
When you don't need or want to sign a message, just erase the signature block manually (it is regular, editable text). Alternatively, use a blank signature (filled with a single space character) as described earlier.