How often, the answer lies in the correct use of reverse; they are a powerful tool for limiting audit ranges to almost any need. See hg help revsets .
In your case, we also use output templates to show only tags, and not the full output of the log of these changes. Thus, if you need all the tags for THISBRANCH:
hg log --rev="branch(THISBRANCH) and tag()" --template="{tags}\n"
Output example for a widely tagged repo
hgsubversion>hg log -r "branch(stable) and tag()" -T "{tags}\n" 1.5.1 1.6.1 1.6.2 1.6.3 1.7 1.8 1.8.1 1.8.2
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