【Answer】Solution: Let the number represented by "cup" be $a$, and the sum of the numbers at the three vertices of each small triangle be equal to $k$. From the given information, we can set up the equation:
$$
6 k=12 \times 2+4 a,
$$
$k=\frac{12+2 \mathrm{a}}{3}=4+\frac{2 \mathrm{a}}{3}, k$ must be a natural number, and $a$ is a natural number from $1 \sim 9$.
When $a=1, 2, 4, 5, 7, 8$, $k$ has no solution; when $a=6$ and 9, the sum of the 7 numbers will be greater than 12, so it is not feasible. Only when $a=3$, $k=4+2=6 ; 1+2+3=6,1+2+1+2+1+2+3=12$, which meets the requirements;

Answer: The number represented by "cup" is 3.
Therefore, the answer is: 3.
12. In the figure, each Chinese character in the circles represents a number from $1 \sim 9$, and different characters represent different numbers. The sum of the numbers at the three vertices of each small triangle is equal. If the sum of 7 numbers is equal to 12, then the number represented by “杯” is . $\qquad$