While in sketch, place a centerline (not an axis). These are in the line flyout. These can be used as symmetry lines for mirroring in sketch mode, as well as construction lines for dimensioning to... they have a lot of uses.
yeah i know all about the symmetry constraint, but in solidowrks you can just draw half the sketch, put a centerline, then click the entities on one side and they appear on the other with the symmetry constraint already there. it saves a lot of time, and i was wondering if it's available in wildfire.