The square is called the 'preserver's sign' by classical palmists. It intervenes as a protection, a framework, a safeguard. Where it appears, it attenuates what other signs might indicate as difficult.
Rarity: Visible in about 15% of palms. Cleaner equals more powerful.
Protection square
When a square surrounds a break or island on a line, it 'repairs' the effect of that break. The period concerned stays difficult, but it breaks nothing, you cross without rupture.
It's a particularly precious sign on the life line: it indicates that a fragile period will be crossed without lasting damage.
On the mounts
On the mount of Jupiter: natural moderation in ambition, you don't endanger yourself to succeed.
On the mount of Venus: protection in affective bonds, ability to choose healthy partners.
On the mount of the Moon: protection against emotional imbalances, solid footing even in inner storm.
Independent square
A square touching no particular line indicates a reserve of strength. You can count on resources others don't have.
If you're crossing a difficult period and see a square on the corresponding zone: that's exactly what tradition calls a protection.