Going to a wedding? You might have the great idea not to sign the guest book as soon as you get to the reception. Wouldn't it be greater if you signed it later in the night, say at 10? Yes, yes it would. However, depending on your activities that night, you may forget to do so! So, what do you do... Simple.
Sign the guest book twice! Once at the start of the night, and once while plastered! Everybody wins!