*ALL* devout male Sikhs usually adopt the surname of Singh (Lion in Hindi). It is actually part of traditional Sikh religious belief, as much a part of the devout, practicing Sikh as the kirpan (dagger) on his person.
That there exist Sikhs who do not follow this tradition is a fact not unknown to me, but the majority of practicing Sikhs do follow this tradition, so much so that whenever I hear someone has the surname of Signh, I pretty much assume that the bearer of the name is a practicing Sikh (yeah, I know I *could* be wrong, but more often than not, it holds true...)
the infowarrior
Yes, I have run into several non-Singh Sikhs.
And some not-Sikh Singhs.
Sikhs tend to emigrate at a much higher rate than other Indians (I think that 1/3 or more of all of them live elsewhere) so outside of India they seem to exist in larger numbers and have a greater presence than they do in India proper.
There aren’t really that many Sikhs, under 2% of the Indian population.