“This will be the sign to you that it is I who have sent you: When you have brought the people out of Egypt, you will worship God on this mountain”. 

Ex 3:12 NIV 

A sign can be many things. It can point out a route to a place – or tell you how fast you can go. It can be a symptom of illness that a doctor looks for when examining you. It can be a mark to indicate a person’s identity as on a cheque. Then shops and tradesmen put signs up to indicate that their business is carried on in a certain building. If you “sign on” you commit yourself to something. Some people finish their day’s work and “sign off”. 
God knew that in the long and arduous journey the Israelites would make from slavery in Egypt to freedom in Canaan they would often wonder whether it was all worth it or whether they would ever get there. In particular they would doubt whether in fact God was in it at all – or whether Moses had led them on a wild goose chase. So God made Moses understand that the mountain called Sinai (also Horeb) would confirm for him (Moses) that God was still guiding and directing the whole venture. The sign was for him alone but when they got there and worshipped God all of them would take part. 
Many disciples of Jesus look for signs that he is with them, guid- ing and helping them – or warning and protecting them. Going for- ward in faith they sometimes wonder if the way they are taking is God’s path – or whether they have been guilty of wishful thinking. You are right to seek God’s confirmation – and to be obedient to him at all times. 

Lord, make your way plain and clear at all times.