I read through the following http://www.mosinnagant.net/finland/m28-rifle.asp  but it is still not clear.  Not sure if I am missing it or just not following.

I am hoping to find a stamp of sorts to state that a rifle is a M28-30, but can't find it. It is almost as though a rifle is designed a M28-30 based on what parts are on the rifle and not by a specific stamp.

If you were looking through 100 rifles, what would you look for to clearly signify if the rifle is a m28-30?

http://7.62x54r.net/MosinID/MosinM2830.htm

Quick way is it looks like a M39 but the upper barrel band is differant.

Front barrel band
distance between barrels bands (shorter on the M39)
Sling swivels on the M39 vs. Slots in the M28/30 stock
More barrel after the sight on the M39.
M28/30 has screws that go into the side of the barrel bands vs. the "swing" bands on the M39.

They're subtle at a distance and can look very similar. I misidentified a M39 at the last show. HARD to see the differences when someone's carrying it around.

Thanks for the feedback. My assumption seems correct in that it appears to be a bit more involved than simply spotting a single mark.

Here are some identification points

M28-30 compared to M39
- The stock is a lot thinner, especially in the front, in the 28-30 than in the model M39.
- if it has the K31 -style aluminum barrel front end bushing it's a M28-30, however, these were often removed in re-arsenaling
- no pistol grip, though early M39's did not have those either
- Front- and back barrel bands are different, and screws go "through" the stock (in M39 the screws won't).
- Front barrel band is a single machined piece as opposed to M39's swivel design
- M28 has usually a little thicker barrel than other Finnish models

M28-30 compared to M28:
- M28-30 has the Finnish  rear sight, similar to M39,  as opposed to M28's modified Russian
- the M28's front sight has no adjustment screws, however, early M28-30's did not either
- Later M28-30's should have the HV (jamb free) magazine
- stocks are almost identical, both were usually altered from Russian Mosin stocks

There are two basic features that distinguish an M28-30 from other variants at first glance.  The stock will have the thin long forarm very similar or identical to an M28 or M27, but unlike the thicker M39 forarm and its more far forward barrel band.  The rear sight will look like the rear sight on an M39.

There are obviouly more  differences and several variations in the features of M28-30's, but the above is all you need to know to spot one.

Also, don't forget that some M28's were upgraded with M28-30 sights and at first glace will look the same as an early M28-30.  These are extremely rare and very valuable as far as mosins go.  The easiest way here to tell the difference is in the barrel shank marlings.  M28's have different serieses of barrel shank markings than M28-30's.

This is mostly true and accurate, however, not 100%. I personally own a M28-30 that has a too low serial number and some other markings that should not be there. The explanation is, that the rifle "started" as a M28 and was later upgraded to M28-30, presumably paid by a private civil guard member.