Heya palmeiras!
Aye, to echo kemiyun - there's absolutely no standardisation amongst the test and measurement gear out there. Generally though, I've found the manufacturers spell it out for you in no uncertain terms on the front panel. Take for instance, the two different R&S instruments on my bench:
The VNA can tolerate a DC component present on the input port (up to 30V), whereas the spectrum analyser can't. (VNA's generally allow a small DC bias in order that active devices under test can be biassed to their appropriate operating points). I've found a series DC blocking capacitor to always be sufficient for my spectrum analysis measurements, bearing in mind that the capacitor forms a single pole RC high-pass filter with the (nominally 50 ohm) input impedance of the analyser [which can catch you out with LF measurements!]
As to the maximum allowable peak-to-peak input voltage - assuming a single frequency sinusoidal input, this is given by:
Vpp(max) = sqrt(0.4 * 10^(dBm/10))
(Which is simply the end result of rearranging P=V^2/R, and the relationships between dBm and power, RMS and peak)
Thus, for the two instruments shown, my VNA can tolerate 14.1 Vpp [superimposed on up to 30V of DC offset], and the spectrum analyser 20 Vpp [with no DC component].
Hope that helps