The time intervals for each letter flashing are \( \frac{1}{2} \), \( \frac{1}{4} \), and \( \frac{1}{8} \). To find the least time, we calculate the least common multiple (LCM) of these intervals:
\[
\text{LCM} \left( \frac{1}{2}, \frac{1}{4}, \frac{1}{8} \right) = \frac{1}{8}.
\]
Thus, the full name of the bookstore can be read again after \( 73.5 \, \text{s} \).