My feeling is that it is not untrue to Shakespeare to repunctuate congruent with your purpose. It seems to me that excerpted quotes which are required to stand alone due to context, in this case a plaque, can legitimately take a period as a reflection of the fact that they must, indeed, stand alone. This quotation is valid on its own when excerpted this way, and a period would not markedly alter or be disrespectful to the original complete quotation, so I would be comfortable with a period, as I have to believe even Shakespeare would be.
If, on the other hand, there were some characteristic of the quote that, due to its substance, strongly implied that the remainder of the quote has to be kept in mind so as not to make the quoted portion incomplete or awkward in any meaningful way, then I would go with an ellipsis. In this case, I think this consideration does not apply. Furthermore, I think the act of quoting this particular partial statement has occurred so many times throughout history that it has become very well accepted as a complete statement.
Finally, a plaque does not necessarily have to have conventional punctuation. It would be perfectly reasonable to have NO punctuation mark at the end of this quotation. Remember that punctuation is essentially (in my opinion) used for pretty much (if not exclusively) two things: To reflect the rhythms and patterns of natural speech, and to disambiguate meanings. Neither of these goals is really necessary when a wall (or whatever) displays a plaque that exists for the purpose of floating a concept, axiom, motto, symbol, or the like, in the minds of those who encounter it ever so briefly. If we carve "Excelsior" into the stone of a library facade, does it need punctuation?