How many different signals can be made by hoisting $6$ differently coloured flags one above the other, when any number of them may be hoisted at once?

Here the flags are placed one above the another so, the order is important => we will be using permutations
We can hoist flags $1$ to $6$,
${=}_1^6\text{P}{+}_2^6\text{P}{+}_3^6\text{P}{+}_4^6\text{P}{+}_5^6\text{P}{+}_6^6\text{P}=1956$ ways
Hence, option 'A' is correct.