A document is being discussed:
"I am about to sign my name, you observe, at the foot of the articles which Mr Chuckster will witness; and placing my finger upon this blue wafer with the vandyked corners, I am constrained to remark in a distinct tone of voice--don't be alarmed, ma'am, it is merely a form of law--that I deliver this, as my act and deed. Mr Abel will place his name against the other wafer, repeating the same cabalistic words, and the business is over. Ha ha ha! You see how easily these things are done!' "

Source: Webster's Revised Unabridged Dictionary (1913)

Vandyke \Van*dyke"\ (v[a^]n*d[imac]k"), a.
Of or pertaining to the style of Vandyke the painter; used or
represented by Vandyke. ``His Vandyke dress.'' --Macaulay.
[Written also Vandyck.]

Vandyke brown (Paint.), a pigment of a deep semitransparent
brown color, supposed to be the color used by Vandyke in
his pictures.

Vandyke collar or cape, a broad collar or cape of linen
and lace with a deep pointed or scalloped edge, worn lying
on the shoulders; -- so called from its appearance in
pictures by Vandyke.

Vandyke edge, an edge having ornamental triangular points.
Vandyke \Van*dyke"\, n.
A picture by Vandyke. Also, a Vandyke collar, or a Vandyke
edge. [Written also Vandyck.]
Vandyke \Van*dyke"\, v. t.
fit or furnish with a Vandyke; to form with points or
scallops like a Vandyke. [R.] [Written also Vandyck.]


Perhaps "triangular ornamental points" may be the meaning.