Pretty much everyone I know takes a photo of their child on their first and last day of school. Whether it's Kindy or Year 4 you want to capture that moment. Later on when they are grown adults it may be hard to remember what year that photo was from (unless your mark etc) so i think its a great idea to get them to a hold sign.
You can print yours on standard paper, colour paper or go a little different and use a chalkboard. I purchased this one from Typo and painted the frame a nice bright colour - lime of course! You can make your own using an old photo frame. Remove the glass and paint the board in black board paint. Or simply paint some mdf. Alternativelymyoi could print a sign or handwritten on card.
Here is my boy on his first and last days on Kindy. Only a few more weeks til he will be holding this sign for Pre Primary! It's amazing the difference in one year