What would be the start signal and stop signal for DNA replication?

It's been a while since I took basic cell bio, but I seem to recall that start and stop signals (or codons) refer to mRNA transcription codons. DNA replication is initiated during the S phase of the cell cycle and you would thus replicate the entire chromosome.

Unless you are referring to intracellular signals?

Start signal is apallandromic site where Sigma factor
combines with the template strand.
Stop signal is rho factor when this is encountered
replication stops

is it DNA polymerase?

Initiation of replication depends on origin of replication sites that are bound by origin recognition complexes which are able to recruit various other required proteins to the site. Since eukaryotic chromosomes are so big there are many origin of replications on each one.

As with the rest of the cell cycle entry into S phase depends on the expression of cyclins that activate Cyclin dependent kinases. Cyclin expression is regulated usually by extracellular signals. I don't know which types of signals directly regulate cyclin expression but examples of growth signals include all of the following:

-steroid hormones binding to their nuclear receptors which can activate transcription
-Increase in intracellular Ca2+ levels which has many effects one of which is to activate calcium dependent kinases like calmodulin
-Production of cAMP which can activate PKA and CREB
-Activation of other nuclear growth factors like NFkB
-Signalling through the mitogen activated protein kinase cascade (MAP-K)

Signaling by these can lead to activation of G1 and G1/S cyclins which can lead to the destruction of inhibitory proteins such as retinoblastoma protein, Hct1 and p27, and increased expression of S-phase cyclins and other molecules required for replication.