The full text is as follows and can be seen here:
"Out of respect to what we believe is a strong and growing public sentiment, we sell revolvers and pistols only to such persons as are legally entitled to carry them. We, therefore, cater exclusively to the wants of policemen, sheriffs, deputies, marshals, game wardens, express and bank messengers and officers of the militia and national guard, and ask that intending purchasers furnish us with evidence that they are legally entitled to the possession of such firearms."
A followup: What law or jurisprudence are Sears referring to in saying that only police and so on are entitled to carry handguns? And where do the bank messengers come into it? Was there, perhaps, a law specifically authorising bank messengers to go armed to defend the cash they presumably carried? This seems like a fairly large change from the modern jurisprudence surrounding the 2nd Amendment.