Hi! It stands for 'silkie feathered green-egger'.
Here are 2 pullets from same eggs / cross that should be laying any day now:
They are the only ones I've hatched that have decent crests.
And the eggs (marked 'S'):
They are a little bigger than the full Silkies and of the 3 I have in the brooder --- 2 have 5 toes and 1 has 4.