Safety pins, and if you are riding in a CTT event, you must pin the small number on your left arm and the large number on your lower back/upper arse so it is visible from the rear when riding in your TT position!
http://www.cyclingtimetrials.org.uk/Information/Procedure/Regulations/tabid/79/Default.aspx - Point 16.
Unless he is pretty quick, he won't be number 1. Start numbers usually correspond to a seeding pattern with 0's and 5's being the fastest, then 1's and 6's etc etc down to 4's and 9's who are the slowest, i.e. the fastest riders go out on the hour, 5 mins past, 10 mins, 15 mins, 20 mins etc, slowest riders set of at 4 mins past, 9 mins past, 14 mins past, 19 mins past etc.