In the UK, it would be a warning sign, thus it would be a Triangle.
Yes, have you seen the falling rocks sign on the trail?
The nouns in the sentence are: sign, drivers, rocks, and street.
When driving in the mountains, you will often see signs along the street that warn drivers about falling rocks.
bears, snakes, Falling rocks , Cliffs
Falling rock signs indicate the possibility of rocks or debris falling onto the road from the surrounding cliffs or slopes. Drivers should be cautious and stay alert for falling objects in these areas.
An octagon would be the shape of a stop sign.Stop has 8 sides and so does the octagon.
A stop sign is in the shape of an octagon.
A stop sign is octagonal in shape.
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The shape with six edges is a called a hexagon. Examples of a hexagon would be a stop sign on the road.
The verb is "warned." It's the past tense of "to warn." But be advised that some signs do not have verbs at all: they just have fragments like "no passing" or "school zone." And as others on this page have noted, "falling" can be a verb, but in the sentence you asked about, it is not--it's an adjective that describes "rocks."
Yes, have you seen the fallen rocks sign on the road ahead?