When starting mobile UX projects, I often found myself using my ATM card to draw out rectangles to represent a smartphone screen. I came across a post on The Russians Used a Pencil for an iPhone stamp to help with UI/UX sketching. I used the file to have a rubber stamp made locally about $38 and $15 for a stamp pad. The stamp outline is made to fit Field Notes or larger sketchbook. You can download the image file below and had a high quality stamp made locally in Toronto at Unique pages – www.uniquepages.ca