You should consider adding tokens like the following:

--%version --%
--%modifications --%

When you check out the latest version of a SQL Script, Source contral would replace a token in the script with the version history from the repository.
When the script is checked it additions made in the modifications token are grabbed and included in the comments box for check-in.

In addition the modification comments could be formatted a little better either by discreet fields or by a masked format.
Make the message concise and informative. I use the following format:

[bug/issue number] [Area of Focus] [Action completed]

Ticket: 199112 Datamart - Updated spCustomer to filter for zipcode

Reference to tracking systems

More detailed information is always necessary. Referencing your commit to issue tracking system not only a good idea, but cuts down on the amount of information you need to include in your commit message.

Area of Focus Label

Culling through a massive list of commit messages is hard enough, providing a focus area to filter your commits makes things easier. Determining what labels to employ is subjective, but having them saves a lot of time.

Action completed

I use the elevator pitch technique when describing the action completed. Imagine getting into an elevator and having to describe the code you are committing to repository in the fewest words possible without using technical jargon.

Perhaps -- # would be a better token, whereas % could trip up some XML parsers.

Examples:
-- #author Jim Smith
-- #version 1.1
-- #desc Listing of customer addresses
-- #mod #author Frank Jones - #Comment