Just added in a checkin from Kiln to a case which included a UK pound sign (£) but it is rendered in the "show checkins" pop up as a diamond with a question mark in it.
Originally posted in the fogbugz forum: http://fogbugz.stackexchange.com/questions/4817/uk-pound-signs-are-showing-up-funny-in-checkin-list
Screenshots as requested:

I can recreate this on my machine doing the following:
- Create a new text file
- Add it to your HG repos
- Commit with message "Testing out £'s in messages"
- Push to Kiln
- Check repos explorer in TortoiseHG and message appears as it should
- Check in Kiln and pound sign is encoded as blue diamond question mark as show in screenshots
If it helps I'm in the UK (running XP Pro SP3) as is our server (IIS7, Win2008 I believe). Checked in Chrome 5 and Firefox 3.5 with same results.
If you need any settings let me know where to find them and I'll get you what I can.
Cheers
Pete