I just emailed my MP the following letter:

Dear David Lepper,

I would just like to thank you for signing Auston Mitchell's Early Day Motion 1155 Photography In Public Areas. I have been increasingly concerned with reports of police action against innocent photographers, including most recently a man assaulted by several security guards in Stoke (http://www.flickr.com/photos/happyaslarry/2420960125/). I'm sure you appreciate Brighton's reputation as an artistic city and your support for this motion shows your continued support for the photography community in Brighton.

Yours sincerely, David Pashley

If your MP hasn't signed this EDM, I recommend you contact them to urge them to sign it and if they have, contact them again to thank them.