Thalassicus had a nice thread on this
here. There was some discussion there about Hungarian notation versus "camel case" notation for variable names. I find a strict adherence to Hungarian very annoying and uninformative. Knowing variable type has never been a problem for me. E.g., x,y are always integers. Much more informative to have recX, recY, hexX, hexY, which actually does tell me something I need to know. An i prefix there is superfluous.
As you noted in the other thread, Firaxis is not consistent with itself on many things. The best you can do (if you use them for a guide at all) is sort of follow what they usually do. Even that might not always be the best idea.
I believe Firaxis uses "g_" for file locals rather than globals in most cases, at least in the UI files. (But since many UI files run in their own state, this may be a distinction without a difference.) Anyway, I followed that convention and then was forced (not quite happily) to use "gg_" for actual mod globals. Since my mod also has certain global tables that are preserved through save/exit/reload, I came up with a third prefix (just "g") for those.
Firaxis uses iPlayer and playerID very interchangeably. If you feel you have to use Hungarian notation (yuck!), then you should use the former only. I settled on a rule for my own mod which was that iPlayer, iUnit, iPlot, etc would always be used for indexed game objects. However, buildingID, policyID, unitID, etc would always refer to ID for any database item. Then you can use buildingType, policyType, unitType to refer to the Type field in the DB (a string; and no, I will not use an "s" prefix). Firaxis often (not always) uses buildingInfo, policyInfo, etc to refer to the whole row in the DB, which I follow. The ID/Type suffix is totally consistent with the DB (which I find most helpful) but, as a consequence, is inconsistent with many of the Lua function names (where "Type" always means database ID: e.g., plot:GetImprovementType(), unit:GetUnitType(), etc.). But as I mentioned above, trying to be consistent with Firaxis is like chasing your own tail.
Edit: Btw, are you offering to rewrite my mod's 20,000 lines of Lua once a standard is determined?