It is one of the upgrade rear bands, only Simson and HZa Spandau made them. It would have been marked like this when made, not necessarily the installation. It was designed to give more surface area to this load bearing surface. As anyone who has owned a G98 will testify, the original narrow band sometimes slips loose the spring and under load can marr the stock around this point. I am sure the extra metal keeps it from, or less prone to, breaking.
I assume this band matches? If it doesn't it is unrelated, though the spring holding in place would also suggest this was the original configuration. It does lend some credibility to the "guess" that this was HZa Spandau done; while these bands were supplied to others the combination of the weird stock acceptance and this band does support this scenario. Depots, especially small fries, didn't usually add the E/H (in the Republican era they did, you often see E/H, E/M or E/P, this is why I think a big depot might be behind this, but HZa Spandau is usually proud of their work and probably the most prone to marking the stock...), though I would still tend to hang my hat of these E/H and nazi eagles were applied at different times (though I can't see a good reason why)