There's always been a bit of fuzz around the issue of on-topic-ness of math (and engineering, but that's a discussion for another day) type questions on our site. Many questions which are in content strictly mathematical would best be answered by a physicist because either the math topic is known mostly to physicists, because the asker is interested in the mathematics mostly as it relates to a physical system, or because the asker wants a physicist's perspective on the math itself.
From one point of view, the fact that a physicist's answer is wanted doesn't matter; math questions belong on Math.SE. This is unsatisfying though, as those who frequent Physics.SE do not necessarily frequent Math.SE, so good answers for the type of question described above may be difficult to obtain if we just post such questions to Math.SE (or migrate them).
What combination of the following strategies should we use to draw attention to their physics-oriented, yet strictly mathematical in content, questions:
Post to Math.SE and advertise the question in chat.
Campaign to get users of Physics.SE to subscribe to the Physics and Mathematical-Physics tags on Math.SE.
Provide a link on Physics.SE to Physics tagged questions on Math.SE.
or any other ideas.
In summary, what can we do to keep strictly math questions off Physics.SE while encouraging our users to answer those questions on Math.SE?