How effective is sulfur in detecting mercury vapors
The vapour pressure of mercury is appreciable, but the evaporation kinetics are slow.  In a well-ventilated lab there shouldn't be concern about mercury poisoning from broken thermometers, Schlenk lines &amp;c.

That said, there is Alfred Stock's famous review (Angewandte Chemie, 1926) on mercury poisoning.  He suffered from a chronic case of mercury poisoning, which IIRC really took off after the war, when they had to save on ventilation.  In old laboratory buildings the quantities found under the wood flooring during renovation are at times staggering.  Our safety guys liked to show pictures of puddles.

To detect mercury there are commercially available detectors, usually build around the resistance of a vacuum-deposited gold film (a few 100 atoms thick).  A low-pressure mercury lamp might also work.