I did this for Trader Joe's in November 2003, when I had been working there for only one month. In those days I was encouraged to do fanciful and amusing signs advertising various products, including vegetables, since TJ was expanding its offering of fresh produce. I did these in markers, laminated them, and mounted them near the item it was advertising. Some of them lasted quite a while. But in later years the style changed and our signs are less "illustrative" and more in the conventional "headline and text" format. Fortunately I was able to scan and save all the signs I did, since the originals faded or got destroyed in the store environment. Trader Joe's still sells plenty of Portobello mushrooms.
"Portobello Mushrooms" was markers on Bristol board, about 9" x 6", November 2003.