Select the Rectangle Tool, create a box like the image below. Go to Effect > Distort & Transform > Zig Zag.
#Zig zag Options
When the Zig Zag window popups, check Preview to preview the result, enter Size=1, Ridges per segment=26, then click OK.
2. Add Drop Shadow effect
With the path selected, go to Effect > Stylize > Drop Shadow, and enter the following setting: Opacity=50, X Offset=1 Y Offset=2, Blur=3, and select black color.
3. Place in your artwork
Now you can remove the stroke color and place in your artwork and align them center.
That’s it!
***Bonus Tips***
If you are creating this stamp for print, make sure your Document Raster Effects SettingsEffect > Document Raster Effects Settings. If you are designing for web/screen, leave it as 72dpi because higher dpi takes more memory.
