if the stop sign is a regular octagon (what I will assume it is), all the sides are equal. so the distance between the points N and T is the same distance that between the points I and Q, or O and U, or N and E
So the triangle is between the points:
N - T
T- E
N - E
and as I said before the distance between N - T and N - E are equal.
two equal sides, so the answer is: isosceles