As it occurs in 1783, I think that it's probably to record payments of stamp duty. In that year the government put a 3d tax on all baptism, marriages and burials to help pay for the costs arising from the American War of Independence..It was repealed in 1794 . It was very unpopular and baptism rates dropped. (You couldn'd avoid burials and marriages were one off events but 3d for a baptism was a lot for a labouring family at a time when income was probably reduced and expences increased) People on poor relief were exempt from payment.
At a guess, e would stand for exempt and r for received. Many registers have a p (poor or pauper) for those that were exempt.
(Can't check to see if it starts in 1783 and ends in 1794 as the pdf doesn't have any earlier pages or pages after 1791).