..two things:
1. Soft rest- pull out your battery while the phone is turned on. Wait 5 seconds and put it back in.
2. Reset Theme- Go to Options> Theme> Push the Blackberry key (the hard button with the dots on it)> select Reset Theme Defaults. This will reset all changes you've made to your theme, but you can change them back.
i have a seperate folder set up with all my messaging icons (sms, email, messages, etc) and stopped getting the symbol. i was getting it for a while but all was fixed when i put it in a seperate folder.