Whilst a lot of tab does have the H and P letters to indicate a hammer-on or pull-off, I have come across tabs which just show the curved line.
The way to tell, in this case is, if the second note is a higher pitch then it’s a hammer-on; if it’s a lower pitch then it’s a pull-off.
And, of course, if it’s the same note, then it’s a sustained note.
Cheers,
Keith
Your timing is both impeccable and slightly eerie Richard 
I’ve been working on Module 10 of Grade 2 this past week where Hammer-ons are introduced! Thanks for the detailed breakdown and examples, I really appreciate it 
Let’s see if I’ve got it:
Pull-off > Pull-off > Hammer-on > Sustain > Hammer-on > Sustain
@Majik Thanks for the extra tips Keith That makes sense, much appreciated.