A reverent place
If you choose to venerate an icon, people commonly kiss the hand, feet, garment, or edge of the icon rather than the face. The exact custom can vary, and some icons are placed in a way that makes one spot more natural.
Watch the parish
The simplest approach is to watch how parish members venerate the icon. If the icon is behind glass or difficult to reach, a bow or the sign of the Cross may be enough.
Why the gesture matters
The point is reverent honor, not technique. A careful bow made with understanding is better than a rushed gesture done only to blend in.
The face in an icon represents the person, so many people avoid kissing the face directly. Veneration should be gentle, clean, and attentive, especially when many people will approach the same icon.
The same principle applies if an icon is behind glass or set in a crowded place. Bow, make the sign of the Cross, or kiss the edge reverently. The meaning is honor shown through the image to the person represented.
The gesture should preserve both devotion and care for the icon used by the whole parish.
When in doubt, a bow with the sign of the Cross is reverent and simple.