Gmail – Filter Messages with No Subject

From the "About Gmail Search" documentation:

Gmail doesn't recognize special search characters like square brackets, parentheses, currency symbols, the ampersand, the pound sign, and asterisks.

As you appear to have already discovered, and my quick tests appear to confirm, this seems to include the exclamation mark character.

I would assume that the regular expression Google are using to match search queries with possible results simply excludes all special characters and operates only on "word characters" (you can somewhat confirm this by the fact that searches for the underscore character, _, do work - the underscore is treated as a word character in a regular expression).

Googles help article 7190 lists the search operators you can use in Gmail. This article lists the AROUND keyword mentioned by RADA.

Currently, using the * (SHIFT 8) also works. I use it as *=AnyTextHere.

e.g. "Ticket* for user" find Ticket 1 for user and Ticket 2 for user and Ticket 1000 for user.