It may depend what software version you had, though I've used custom software for most of the last 2 years so can't recall what the stock features are.
If you have a version which supports widgets on the lockscreen then you could use something like Zooper, Simple Text or Minimalistic Text to make a widget with your email address.
If you have a version which does not support this (and the latest Android versions do not) I can think of two options:
1) Look for a replacement lockscreen in the Play Store which does allow you to do this
2) Use an image editing program to add your contact info to an image and use that as your lockscreen wallpaper.
I am using a custom ROM which allows me to customise the "carrier name" text on the lockscreen, so I replace that with my email address (not the GMail address I use with the phone - no point helping the bad guys!). But I'm certain that isn't an option with the stock software.