Not much of a difference. Frankly, there has been much ado about nothing. The general belief is that a document which is given an ‘Exhibit’ number is usually held to be legally admissible. For instance, original documents are given the nomenclature of ‘Exhibits’ by the Court and accepted in evidence as ‘Exhibit A’, ‘Exhibit B’ and so on.
However, it needs to be remembered that, this – by itself, does not amount to proof of a document. EVERY DOCUMENT HAS TO BE PROVED IN ACCORDANCE OF LAW – WHETHER IT IS MARKED AS AN EXHIBIT OR A MARK. A document exhibited in evidence may still be taken not to be proved and, therefore, the court may eschew it from consideration.
Marking – similarly, also pertains to simply giving a nomenclature to a document for the purposes of identification. In practice, it is believed (albeit erroneously) that documents which are photocopies or otherwise ‘objected-to’ during recording of evidence (on whatever ground) are to be ‘marked’ and not ‘exhibited’.
However, there is little legal sanction or meaning to it. Merely because a document is ‘marked’ does not make it inadmissible.
The question of admissibility and proof would be decided by the court separately.
Conversely, just because a document is ‘exhibited’ does not mean that it is conclusively taken to be proved or decided to be ‘admissible’.
All in all, marking something as an ‘exhibit’ (Eg : Exhibit PW1/A, PW1/B, and so on) or ‘marking’ it (Eg : Mark A, Mark B, and so), hardly makes any difference as in either case –
i) document has to be proved in accordance with law;
ii) Its admissibility – still – has to be established.
Much ado about nothing, right?
For clarity, read Justice Lahoti’s brilliant exposition on this in Sudir Engineering Company vs Nitco Roadways Ltd, 1995 (34) DRJ 86,