Yes it is forcing.

 

After partner has made a jump to 2nt showing 18/19 points then the only way to avoid being in game is

 

a) pass the 2nt

c) play the wollf sign off convention

 

Given most often responder will want to be in game or make a slam try once partner shows 18/19 the most common question to bw sorted out in responders 2nd bid is 'which game'

 

The usual meaning of the bids in the majors after

 

1d-1s-2nt

 

are

 

3h - I am 5+/4+ in the majors and game forcing+

3s - I have a solid spade suit and slam interest - please  cue bid

4h - I am 5/5 or 6/5 in the majors - pass or correct

4s - I have a stand alone spade suit but I am weak with no slam interest

 

When responder has 5 spades and is not sure if 3nt or 4s is the right place partnerships usuallly use some new minor force or more commonly the wolff convention to ask about  partners major holdings

 

You will find that most bids after partner has made a strong bid are forcing below game - and there isnt a way to sign off (except pass)..