Well, I'm back from my England-Wales borderland excursion. As Wales never really functioned as an independent country before it became attached to England in the UK (it was a loose regional area made up of various tribes), its borders weren't demarcated. Scotland, however, was a functioning nation and did have demarcated borders with England. Likewise, Wales was controlled by England/UK much earlier than Scotland, so Scotland had a chance to mark its borders, while Wales did not.
The only indications of the border are the road signs, which welcome travelers to a new county (shire), although there are some pavement changes at the border, where one local authority begins paving and another one ends. I also found a small stone bridge (very rural area) across a tributary of the Monmouth River, which forms part of the England-Wales border. There was no sign whatsoever that we were crossing the border. The only indicator was that the road sign on the Wales side of the bridge, which read 'road narrows' was also in Welsh. On the English side of the bridge the very same sign was only in English.
While I am a bit disappointed at not finding some old markers, it was a very educational experience. I have a few pics I'll post once they're developed.
Cheers,
Dallen