Both Uses

allude
in
The Adventure of the Speckled Band
(Auto-generated)

Ah, and what did you gather from this allusion to a band--a speckled band?
*

allusion = an indirect reference
When you combine the ideas of whistles at night, the presence of a band of gipsies who are on intimate terms with this old doctor, the fact that we have every reason to believe that the doctor has an interest in preventing his stepdaughter's marriage, the dying allusion to a band, and, finally, the fact that Miss Helen Stoner heard a metallic clang, which might have been caused by one of those metal bars that secured the shutters falling back into its place, I think that there is good ground to think that the mystery may be cleared along those lines.†

Definitions:

(1) (allude)
to make an indirect reference

The expression, no allusion can mean "not even an indirect reference"; i.e., neither a direct nor an indirect reference to something.
(2) (meaning too rare to warrant focus)