Is there a simple command to convert a branch to a tag?

Question

I am about to complete a tedious process of converting \"dumb snapshots\" to git. This process has been going very well (thanks to this rename process), but now I realized that

Answer 1

Per Andy's answer, I've made an alias that can also be used for the same thing:

[alias]
branch2tag = "!sh -c 'set -e;git tag $1 refs/heads/$1;git branch -D $1' -"

Usage

If you want to convert branch bug-2483 to a tag (while your main branch is master) write:

git branch2tag bug-2483 master

UPDATE 1

Changed to reflect the solution proposed by kauppi.