In the context of Laplace transforms, what does the subscript in $h(t) = f(t)\cdot u_3(t)$ signify?

Question

Problem

Note: I do not need help solving this problem (yet), but I'm unsure about notation.

Find the Laplace tranform of the function $h(t) = e^{2(t-3)}u_3(t)$.

Question

What does the subscripted $3$ in $u_3(t)$ mean?

Answer 1

As Dr. MV suggested in the comment, it referred to the right-shifted unit step function.

$u_3(t) = \begin{cases} 0, & t < 3 \\ 1, & t \geq 3 \end{cases} $

Posting this as an answer for the sake of completeness.