Yellow Diamond Shapes

[Jennykenny]

I'm sure this has been asked, and answered before, but what is the meaning of the yellow diamond, (and other shapes) at the side of roads?

[Graham-W]

They are warning signs, usually reinforced by a message or image, but not always.
http://www.123rf.com/photo_5206020_yellow-diamond-caution-duck-crossing-sign-beside-a-road.html

[Graham-W]

Just checked and they are used for emergency diversions on Motorways.
See bottom of page 6 here:- http://www.direct.gov.uk/prod_consum_dg/groups/dg_digitalassets/@dg/@en/documents/digitalasset/dg_070644.pdf

[Jennykenny]

Thanks.