The number of signals that can be sent by 6 flags of different colours taking one or more at a time is given by

By alteration in the arrangement of flags the signals will change. So we have to find permutations i.e. arrangements of flags. We are at liberty to use any number of flags at a time. Therefore the required number of signals is 

$$\begin{gathered} {=}^6{P}_1{+}^6{P}_2{+}^6{P}_3{+}^6{P}_4{+}^6{P}_5{+}^6{P}_6 \\ =6+30+120+360+720+720 \\ =1956 \end{gathered}$$