Unsubtle means so obvious that nobody could miss the point. The hint that was really an instruction.
The word is a criticism, and it is usually aimed at an attempt at cleverness that failed: an unsubtle hint, an unsubtle piece of product placement, an unsubtle attempt to change the subject. That is the key to it — you only call something unsubtle if subtlety was being tried for. A thing that never pretended to be delicate is just blunt or direct. English also has the delightfully unhelpful about as subtle as a brick, which means the same thing with more enjoyment.
Proto-Indo-European
*tetḱ- — to create, produce; to cut, hew
Latin
subtīlis — of texture: delicate, fine; slender, thin; accurate, keen; having fine judgment; etc.
Old French
sotil
Middle French
soutil
Anglo-Norman
sotel
Middle English
sotil
English
subtle
English, today
unsubtle
Built from
From un- + subtle. subtle The is derived from Middle English sotil, soubtil, subtil (“of a person, the mind, etc.: clever, ingenious, penetrating; cunning, sly; insidious; delicate, fine; not dense, light, thin; finely powdered; narrow, slender; etc.”), borrowed from Anglo-Norman sotel, subtil, sutil, Middle French soutil, subtil, sutil, and Old French sotil, soutil, subtil, sutil (“of an object: skilfully designed or made; delicate, fine; slender, thin; of an intangible thing: difficult to understand; of a person: discerning, shrewd; devious, sly; etc.”) (modern French subtil), from Latin subtīlis (“of texture: delicate, fine; slender, thin; accurate, keen; having fine judgment; etc.”), from sub (“below, under”) + tēla (“warp (threads running lengthwise in a loom); web”) (ultimately from Proto-Indo-European tetḱ- (“to create, produce; to cut, hew”), from teḱ- (“to beget, sire”)). The word displaced Old English smēag literally “creeping”. The modern and Middle English (and French) spellings with -b- are influenced by Latin subtīlis; the letter was probably never pronounced. The is derived from Middle English sotil, soubtil, subtil (“wise person; sophisticated people collectively”), from the adjective.
Etymology from Wiktionary, CC BY-SA