In Ai CC2014, you can use the new smart rectangle features.
- Drag out a rectangle with the Rectangle Tool.
- Click and draw on one of the inner corner controls (a tiny circle with a dot) to round the corners.
- Alt/Opt Click on one of the corner controls to cycle through the three kinds of corners.
- Assign your fill color.
- In the Appearance Panel, with the rectangle still selected, click on ADd new stroke (the leftmost tiny button at the bottom of the panel). Set this new path's stroke to, say, 4 pts. Assign the lighter green color.
- To offset the new stroke, make sure it's "appearance layer is selected in the Appearance Panel, and then click on the tiny "fx" button at the bottom of the panel, and select Path and then Offset path... Click Preview so you can see what you're doing, and then set the offset amount to a small negative number (e.g., -5) and the new path will shrink inside the sign.
These instructions are pretty terse, but they should get you started. Feel free to ask further questions.
Have fun!
Allen