Formulae distinguished only by case A recent question (on $\ce{CI}$ v $\ce{Cl}$) reminded of this question: are there any real (as opposed to contrived) formulae which would be the same if case was ignored?

One certain example is $\ce{Co}$, Cobalt, and $\ce{CO}$, Carbon Monoxide.  Of course, confusing Cobalt and Carbon Monoxide is rather unlikely.  

In my search for others, the best example I could find was $\ce{BaS}$, Barium Sulphide, and $\ce{BAs}$, Boron Arsenide.  Are these real substances and is the stoichiometry just $1:1$?  I had trouble verifying that.  

Are there any more interesting examples?

One real example that I saw once was a poster in a university chemistry lab showing some complex organic molecules.  $\ce{Ac}$ appeared at many points but it seemed very unlikely that these compounds contained Actinium.  I then noticed $\ce{Me}$ and $\ce{Et}$ and guessed that they were organic units e.g. methyl and ethyl so $\ce{Ac}$ may have been acetyl.
Letter case in chemical names sometimes matters too! E.g. when o-methylphenol (o-cresol, ortho-cresol, 2-methylphenol, I) improperly capitalized to O-methylphenol (instead of o-Methylphenol), it can be interpreted as a different compound, phenol methylated at oxygen (anisole, methoxybenzene, II).