I have been studying 1887 sixpences for fifteen years and can confirm this as a recognized variety. You should see from the coin that the Rs all have both serifs left and right at the base of the upright so this coin is a variety of the R over I that is in most books. If you look at the R in BRITT: you should be able to see the R/I very clearly. This is a distinguishing feature of this die variety which has come to be called A over A but, as pointed out, it could be an inverted V. The specimens I have do not show a bar to the "A" but you will have noticed how weak the strike is from your own specimen. They turn up from time to time on ebay and fetch fairly normal prices but then most people don't know what they are looking at. In a survey of 1,518 sixpences I have found 5. I don't look for them any more. Extrapolating this would give a mintage figure of 12,107. Given You have one and Nick has one the sample then would indicate 17,000+. It is most likely this pair of dies had a normal use and so the actual figure would be more like 30,000. Well done on spotting it. There is a specimen in The Royal Mint collection RMM8457.