Arthur, in comments on the Mosquito, pointed me to this link:
SIG SAUER, Inc. has initiated a Mandatory Safety Upgrade pertaining to our new Model P238™ pistols. We have determined that a small number of P238 pistols may have safety levers that are not manufactured to factory specifications. Under certain conditions, it may be possible for the lever not to be completely engaged in the safe position. In this condition, the gun will not fire when the trigger is pulled. However, when the safety lever is moved to the off position, the hammer may fall, with the remote possibility that the gun could fire unintentionally, thus creating a risk of injury or death.
The factory page on this matter is here with full information; if you've got one of these, make sure if yours is one of those needing the fix.