All geometry symbols I could think of are compiled on this page. If you did not find the symbol you were looking for, kindly email and I will add it to this list.
Symbols Meaning of the symbols

Therefore

If x then y

is congruent to

is not congruent to

is similar to

Angle with vertex A

refers to angles(more than one)

Measure of angle A in degree(s)
° Degree(s)
n
° n degree(s)

is perpendicular to

is not perpendicular to
|| is parallel to

is not parallel to
∟ right angle sign
∆ABC Triangles with vertices A, B, and C;

refers to triangles (more than one)

Parallelogram with vertices A,B,C,and D

refers to Parallelograms( more than one)

circle with center A
AB Segment with endpoint A and B
AB Length of segment
AB

Ray AB with endpoint A passing through B

Line through points A and B
π Ratio of circumference to diameter of a circle.
s Usually Length of a side
b length of a base
A Area
h height of a figure
d diameter of a circle
r radius of a circle
P perimeter
C circumference
B Area of base
L.A. Lateral area
S.A. surface area
V volume
l slant height
a apothem
b
1, b
2 bases of a trapezoid (parallel sides)
n-gon polygon with n sides

Arc with endpoints A and B

Arc with endpoints A and C containing B

measure of arc AB