Simplest possible way to tell about Sabers vs. Systems Sabers vs Astro Sabers:
For non-display radios:
12 position channel selector = Saber
16 position channel selector = Systems Saber
Presence of an A/B concentric switch located with the channel selector = Astro Saber
That alone will determine the radio family.
For display models:
Orange buttons = Saber or Systems Saber. If it's a Saber, the orange buttons will be labelled MENU, SELECT, ENTER.
Blue/green buttons = Astro Saber
Housing size: All Astro Sabers are a little over 5 inches tall. (Without battery or antenna)
No Saber can be that tall. Sabers are available in two lengths, secure and non-secure versions.
The non-secure version makes a radio that's around 4 inches tall.
The secure version is about another 5/8 inch taller.
Sabers are conventional only.
Systems Sabers support analog trunking. (Usually Smartnet) NO DIGITAL.
Astro Sabers are fully digital platforms capable of handling up to P25 Phase 1 trunking.
Depending on options, of course.
The oddball of the bunch is the rare Saber SI, which looks like an Astro Saber but is the same height as
a regular Saber in the secure version. It is actually an MTSX series radio repackage into a Saber form factor,
and was only made in 800 MHz.
Here's a nice visual reference.