In the default Invoice format, we get the Currency Code/Symbol as a suffix, after the numbers.
Instead of this, can we have the Currency Code/Symbol on Top over the figures?
You cannot do this. The reason is that when multiple currencies are used, the program keeps currency designations for each line item of a transaction. But if you operate in only one currency, you do not need to designate a base currency at all. Then no symbol or code will show.