The "diamond" lane is for carpools consisting of two or more occupants during certain times of the day.
Usually city/regional transport buses.
On a freeway/highway, the lane which contains the diamond like shape is a separate travel lane. Specifically this lane is dedicated to the "ride share" and/or individuals carpooling.
carpool lane
If you mean a diamond on the lane, that means that that lane is for BICYCLISTS ONLY, if you mean as a shape of a sign such as a "slippery when wet" sign, that usually tells you important things. I looked it up in my "Virginia Driver's Manual" and it says a diamond shaped sign is a warning sign.
Stopping or parking is not allowed (except buses).
One large heart diamond beneath a small heart diamond means "Love is forever"
It is found in VERY few areas and it means a change in the road from a 4 lane to a 2 lane road.
A diamond lane on the freeway means it is a special lane on a highway or street that is reserved for a specific type of traffic (such as cars carrying more than one passenger). These lanes are also meant for the drivers who are not exiting any time soon.
Left side lane
driving is not permitted in that lane
Painted
Keep right of where the sign is placed. A sign telling you to get to the far right lane would be telling you to merge right, and would be used either in conjunction with signs indicating the left lane(s) end(s), painted lines which deviate towards the right lane, and barrels and delineators (in instances of a work zone in which lanes are closed off).
A lane is a small pathway. It can alse be used to denote a fixed route, such as a 'swimming lane".