how do I annote a vector on a signal plot

Hello guys,

So i have a signal plot. and then I have a vector that are indexes to some particular events in this signal.

So I want to plot this vector also on my signal. Ideally I want it to look something like in the image below.

The orange is my signal. so assuming I have a vector I want to annote it as shown in the violet crosses.

Note: The crosses dont depend on the y axis.

Answer 1

[KSSV]

A = rand(1,100) ;
idx1 = find(A>0.7) ;
idx2 = find(A<0.4) ;
plot(A,'b')
hold on
plot(idx1,0.8,'+r')
plot(idx2,0.2,'+k')

[fadams18]

awesome, got the idea. thanks!