The red circle with a bar sinister is the international symbol for signage meaning "no" or "forbidden". So that superimposed on the word "rock" means "No rock" or "Rock is forbidden in this area."
Noel
Circle with a line through it is square yards, a square with a line through it is square feet
what a sign mean that has a red circle with rock in it and a red line through it
If you mean a line that gous from the center of a circle to the edge of the circle, that is a radius.
line segment
Do you mean, like, the Earth? The equator. If you mean the line going from side to side across the middle of a circle then... the diameter of a circle
Pi is the equivalent of any circle's circumference (the length around the edge of the circle) divided by the same circle's diameter (the length of the line that runs directly through the center of the circle). Pi is always equal to about 3.14.
A circle with a diagonal line through it is commonly used as a symbol to represent "no" or "not allowed." It is often used in signage to indicate that something is prohibited or unavailable.
A tangent to a circle is a line which touches the circle once. That is, it does not pass through the circle, which would mean intersecting it twice. A way to form a tangent is draw any line from the centre point of a circle to its edge. A line on the edge perpendicular (at 90 degrees to) this line will be a tangent.
A circle is a line, drawn around a point in such a way that the line is always the same distance from the point. This distance is known as the 'radius' of that circle.
Diameter of a circle is a line that goes from one side of the circle, passes through the center of the circle, and touches the other side of the circle. So a circle could have a diameter of length 2 inches, or maybe 7 feet, etc. If the line does not pass through the center of the circle, it is not a diameter.
The diameter is the chord (line that goes from the circle to the circle) that goes through the center of the circle. It is the largest chord. It is also equal to twice the radius.