With iOS 6, we can now add custom signatures for each email account we own, as opposed to being forced to use just one. This is awesome for me and probably for anyone who uses many accounts for different purposes, and it's really easy to set up. I always say that, don't I? Well, in this case, it's actually true. All you need to do is go to Settings > Mail, Contacts, Calendars on your iOS device and scroll down to Signature.
You'll note that that since I only had a single one set, there's a preview of it in that field. But we're going to change stuff around by tapping on Signature and toggling All Accounts to Per Account.
When you do that, you'll get a box for each email account you have. You can choose no signature if you want to by leaving an account's box blank (as I've done with the first one shown above). Add in custom text for each, and then you can format elements of your signature similar to how you do so for text in the Mail app. Just tap and hold briefly to pull up the Select menu, select the text you want to format, and then choose the formatting button pictured below to add bold, italics, or underlining.
(Depending on how much text you've selected, you may have to click an arrow to reveal that option.)
When you're finished making your changes, go back out to the Mail, Contacts, Calendars screen to see that now instead of a preview, you'll get the number of accounts you've configured with custom signatures.
Which can be useful for, well…something, I suppose. I haven't figured it out yet, but I'm sure there's an important reason.