Identify the stars brighter than the least bright planet (among those visible to the naked eye) at its least brightest, namely Mars. We somewhat arbitrarily pick this threshold because the goal is to create a guide for casual naked-eye astronomy from urban areas with a lot of light pollution. Planets are fun to observe because they wander.
This should be easy, though variable stars might make deciding whether a star is brighter than the threshold a little tricky.
Even without variable stars, figuring out exactly which stars are brighter than the cutoff magnitude might be tricky, needing apparent magnitudes to high precision. However, astronomical photometry can be very precise, as demonstrated in the discoveries of exoplanets by transits.
I couldn't find a reliable source giving the minimum brightness of Mars. Among other factors, its brightness is going to slightly vary depending on the weather there.
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