They are referred to in the US as Cardinal buoys/Regulatory marks and are used to regulate certain areas. Regulatory buoys are white, with two orange horizontally orange stripes. Between the stripes you'll find either an Orange circle or diamond. The diamond is conveying a warning. It could be a rock, a submerged object, shoal, wreckage or other danger. The black lettering underneath will usually indicate the danger.
An orange crossed diamond and black lettering indicates an area where vessels are prohibited and only swimming is allowed.
A white buoy or sign with an orange diamond and cross means that boats must keep out of the area. Black lettering on the buoy or sign gives the reason for the restriction, for example, SWIM AREA.
White buoy's with orange markings and black lettering are a regulatory marker for boaters.
Keep out
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morring buey
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informations or directions
Keep out
Crossed diamonds indicate areas off-limits to all vessels such as swimming areas, dams, and spillways.*NOTE that an orange diamond with black lettering within the diamond means a danger exists, such as rocks, shoals, stumps, or dams.
The orange-square buoys give information or directions.
Information, such as direction, distances, location.