Dan got a triangle-shaped poster of a yield sign. The base of the poster is 36 inches. The height is 30 inches.

To find the area of a triangle, you can use the following formula:

\[ A = \frac{1}{2} \times \text{base} \times \text{height} \]

For Dan's triangle-shaped poster, the base is 36 inches and the height is 30 inches. Plugging these values into the formula gives:

\[ A = \frac{1}{2} \times 36 \times 30 \]

Now, calculating further:

\[ A = \frac{1}{2} \times 1080 = 540 \]

So, the area of the poster is:

\[ \boxed{540} \text{ square inches} \]