x <- c("Total Assets in th USD", "Equity in mil EUR", "Number of Branches")
currencies <- c("USD", "EUR", "GBP")

regex <- paste0("\\b(",
                    paste(currencies, collapse = "|"),
                ")\\b")
# results in
# "\b(USD|EUR|GBP)\b"

matches <- regmatches(x, gregexpr(regex, x))
res <- lapply(matches, function(x) if (length(x) == 0) NA else x)
res[is.na(res)] <- ""
unlist(res)