To signalise means to make something clear or obvious, often by using a signal or sign.
Signalising is like making a big point or showing something important.
Examples:
She used a flag to signalise the start of the race.
The bright colors signalise danger.
The teacher used a bell to signalise the end of class.
The big sign signalises the way to the beach.
The fireworks signalise the start of the celebration.
The lighthouse signalises the way for ships at night.