I have this old document originating from 1760 (Spain) and wondered if anybody had ever encountered these symbols / prefix to numbers - in the hope it might help identify the currency in question (Reales/Escudos) Thanks for any tips you might have.

That is very cool. So that symbol to the left where the $ symbol would be in the US represents Reales? I haven't seen that and couldn’t find it on line.
Yes cool and intriguing! At present the first recorded appearance of the conventional US dollar symbol $ is in a New Orleans document written by an Oliver Pollock in 1778. So this document is a decade earlier than Pollock and contains a sort of modified number 8 (being the 8 Reale I suspect) as well as a sort of early gate # symbol. Another theory in the evolution of the dollar symbol was shared by HM Larson in 1939 which suggested the $ was derived from the Greek character “psi” ¥ and an S. This 1760 Spanish colonial document does indeed contain that “psi” symbol. 
The author is a Joseph Luis de los Santos who is a funeral director. The funeral itinerary and his quoted cost of #352 seems likely to be an eighteen century Baroque style funeral.

This is the crown style watermark in the vellum. I have also been looking for the watermark without success.
I read that the $ was probably from the column and ribbon on the 8-Reale, your saying it’s from the Greek letters? I’ve never heard that.
I'm with you but other theories exist. I have had a specialist in Hispanic studies at the British Library look at the document and they consider it authentic. Right now a letter written in New Orleans by an Irishman in 1778 is the earliest noted use of a US dollar symbol, or what would later be regarded as a US dollar symbol. The 1760 Spanish colonial document here pre dates the New Orleans letter by 18 years and shows money symbols like an 8 (but not an 8) but more flourished, like cursive handwriting. These could be a 8 Reale symbol or equally a Spanish dollar I guess. Either way that early 8 symbol is a precursor to what eventually became the $ symbol.
Very interesting this document.
Here is a short Bank of Canada post on the different theories of the origin of the $ symbol.
The book is on archive.org and can be downloaded for free by anyone. Here it is opened at page 61 where the discussion on the symbol $ starts.
The big problem with this book is that it is missing something everyone should learn in high school: Provide your 🤬 references. The author justifies his approach in the preface, but at the time of collecting his data he should have also collected his references. Not surprisingly, the book is home published. BTW the fact that you provided the reference, @771h5, made it easy for me to find it online.
On my side of things I'll keep an eye open when I consult 18th-century Caribbean newspapers. What's interesting with the Caribbean islands is that some of the British colonies went from Spanish to British, and/or used the dollar as their money of account even though they were officially in the "Sterling zone".
If you are new to this particular strand of the subject regarding the evolution of the dollar symbol it can be quite frustrating to hit such brick walls regarding reference material protocols but the more years you spend reviewing scholarly writing the more it becomes apparent that there is no universally accepted explanation between scholars. It may be that Professor Florian Cajori's review of the subject in volume 81 of Popular Science Monthly (December 1912) https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_81/December_1912/The_Evolution_of_the_Dollar_Mark still remains our most (or only) authoritative point of reference. But in the meantime it would be most interesting to hear news of any of your investigations into the Caribbean source material you mentioned.
After Barry Taylor, Head of Hispanic Collections at the British Library recently looked at the 1760 document he has now referred me to Professor Fermín de los Reyes Gómez, Dept of Spanish Literature at University of Madrid. I look forward to sharing more news.
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