I just wrote 'the graffiti was completely obscured'. Then I did a quick internet search to check whether that was correct. 'Oxford Dictionaries' says I'm wrong, it should be 'the graffiti were completely obscured' to preserve the Italian plurality, but the balance of all the references indicated 'graffiti is' to be the most common de facto use by a significant margin.
(Common usage also seems to favour 'scampi is' over 'scampi are', but the margin is much slimmer.)
The correct way to formulate the question I want to ask is eluding my tired old brain, so instead:
Which would you use and why? And for the editors among you, would you do anything if you encountered either in a story?