In The Sign of Four:

Three bob and a tanner for tickets

A bob is a shilling. This term was in use in Britain and Australia right up until decimal currency was introduced, and is still used in some figurative expressions such as “a bob each way”.
A tanner is a sixpence.

hook it

Depart speedily

So help me gracious, I have a wiper in the bag, an’ I’ll drop it on your ‘ead

I am familiar with various things called a “wiper” but none of them is something that, if dropped on one’s head, would damage it. Any clues?

"Wiper” = viper.

Yes, to expatiate, 19th century Cockney substituted W for V and V for W. (Although not universally.)

The nineteenth century saw the first wholesale attempt to record Cockney as it was spoken. The low-life episodes of Pierce Egan’s Life in London (1821) take his heroes deep into the East End and its speech. London’s great chronicler Charles Dickens, notably with Sam Weller and his father, is unsurprisingly keen on setting down the sound of Cockney speech, most obviously in the substitution of ‘v’ for ‘w’ and vice versa. The pioneering sociologist Henry Mayhew recorded his impoverished or criminal interviewees in much the same style.

From OED.

Ha. Thanks.

Sepoy: an Indian soldier working for Britain.

hook it

Depart speedily

Which I have always assumed derives from sling one’s hook; but I could be wrong.

Lascar is another term which often crops up in the Holmes stories, in fact I’m pretty sure that;s where I would have first encountered it as a boy. It’s primary sense is an East Indian sailor. Here’s the etymology from OED:

Either an erroneous European use of Urdu lashkar army, camp (see lashkar n.), or a shortened form of its derivative lashkarī (see lascarine n.). In Portuguese c1600 laschar occurs in the same sense as lasquarim , i.e. Indian soldier; this use, from which the current applications are derived, is not recorded in English (but see quot.

BTW I noticed that in the movie Sherlock Holmes: a Game of Shadows], Holmes uses the phrase “crack on”, meaning get on with it. The film is set in 1895. Is his use of this phrase anachronistic?

Not anachronistic, as witness some of the cites under crack, v. 22a in OED.

intr. To ‘whip’ on, ‘pelt’ along, travel with speed; Naut. to clap on full sail (colloq.)

1837–40 T. C. Haliburton Clockmaker (1862) 43 He must have cracked on near about as fast as them other geese.
1840 R. H. Dana Two Years before Mast xxxv. 133 [We] set the flying-jib and crack on to her again.
1847 Illustr. London News 31 July 74/2 The trio coming..as hard as they could crack.
1867 W. H. Smyth Sailor’s Word-bk., To crack on, to carry all sail.
1890 W. C. Russell Ocean Trag. II. xix. 126, I doubt if anything will hinder the Colonel from cracking on when he catches sight of us.

"Biassed”
(The Boscombe valley mystery)

Biassed is an alternate spelling still seen today (at least here in the UK).

Do the two esses look odd to you, OP Tipping?
How about “nonplussed” or “focussed”? One “s” or two?

You certainly seem to be giving the works of A.C.D. a thorough going over. Have you noticed the anomaly in one of the names in “The Sign of Four”?

Biassed is an alternate spelling still seen today (at least here in the UK).

Really? Well there you go. I don’t think I’ve ever seen it before. It would be regarded as a plain error down my way.

lioniello: focused is the form I’d use. The (quote)rule(unquote) that is applied in Aust is that you don’t double the final consonant of the polysyllabic verb if the last syllable isn’t bear stress. Biased, budgeted, developed, benefited, focused etc. The exception (shrugs) is the l. If it ends in a single l, we double it. e.g. signalled. The exception to that is parallel. Maybe someone thought “parallelled” just had too many damned ls, which is a pity because it nicely looks like what it means.

No doubt there are other exceptions. The stress in nonplus is fairly evenly distributed so I wouldn’t consider it to be an exception to the above.

What anomaly in TSOF do you refer to?

The OED says, “in inflections, often spelt biasses, biassed, biassing; though the single s is more regular.”

("Spelt" in that quote throws me too.)

OK, OK. But --- if we were discussing a pair of Siamese twins with only one head and two tails, I would say that they were biassed (and of course, if they had two heads and only one tail, they’d be half-assed).

“The Sign of the Four - Jonathan Small, Mahomet Singh, Abdullah Khan, Dost Akbar”.  The anomaly is in the name “Mahomet Singh”. “Singh” is a name used by all Sikhs, and by some Hindus of various denominations, but not by adherents of other religions. “Mahomet” (or, as it is more commonly spelt nowadays by English speakers, “Muhammad") is a name used only by Muslims. I do not think that the two names would be used by one person. Of course, I could be wrong. If so, I shall welcome correction.