Let \( x \) represent the number of signs each volunteer received.
Since Joanie gave the same number of signs to each of the 4 volunteers, the total number of signs given to the volunteers is:
\[ 4x \]
After giving out the signs, Joanie had 8 signs left. Thus, we can write the equation:
\[ 72 - 4x = 8 \]
To solve for \( x \), we first add \( 4x \) to both sides of the equation:
\[ 72 - 8 = 4x \]
This simplifies to:
\[ 64 = 4x \]
Next, we divide both sides by 4:
\[ x = \frac{64}{4} = 16 \]
So, each volunteer received 16 signs. To check our work, we can calculate the total number of signs distributed and ensure it adds up correctly with what Joanie has left:
- Total signs given to volunteers:
\[ 4 \times 16 = 64 \]
- Signs left with Joanie:
\[ 72 - 64 = 8 \]
Since Joanie has 8 signs left, our calculations confirm that the solution is correct. Therefore, each volunteer received:
\[ \boxed{16} \] signs.