What do the stars located in the top left had corner of each post represent?

Member rank.

Gold stars are members of the moderating/administrating team, and orange are gearheads.

They represent your "status." The higher your post count, the more stars you have. Yellow and orange stars indicate club staff.

LE Member 0 - no star
SE Member 10 - half star
SLE Member 25 - one star
SSE member 100 - 1.5 stars
SSEi Member 150 - 2 stars
GXP Member 200 - 2.5 stars
Posts like an LG3 300 - 3 stars
Posts like an LN3 400 - 3.5 stars
Posts like an L27 600 - 4 stars
Posts like an L36 800 - 4.5 stars
Posts like an L67 1200 - 5 stars
Posts like a Northstar 1500 - 5.5 stars
Certified Bonneville Nut 2400 - 6 stars