However, depending on the context, you could use:
* Reg. - This is a common abbreviation, particularly in business or administrative contexts.
* Rgn. - This abbreviation is less common, but still understandable.
* Region. - Sometimes, you can simply use the word "Region" followed by a period to shorten it.
It's best to choose an abbreviation that is clear and understandable to your audience. If you're unsure, it's always best to spell out the word "regional" in full.