This was a question I recently received from a client. Simple answer is “No”.
It is true, that most artists do. This includes early artists, such as Philippe Ledoux, Xavier de Poret and Henry de Linares.
But then there is Hugo Grygkar, who designed the very first Hermes scarf, Jeu des Omnibus et Dames Blanches in 1937 and so many others.
Monsieur Grygkar never signed any of his creations. Christiane Vauzelles preferred to leave her 26 designs unsigned including her Caraibes.
Now it can also happen that you come across a scarf, that you know was originally signed but this one lacks the signature.
A perfect example of this is the ever-so-popular Astrologie (also known as Dies et Hore because that is what it says on the scarf itself and it is commonly assumed that that is the name of the scarf.
Artist: Francoise Faconnet
Year: 1963, 1970s, 1980, 1988, 1999, 2003, 2008, 2010 (as Dip Dye 90cm)
What I have come across is that seen with some re-issuesthe signature on a re-issue or the signature, originally in black ink now on a particular reissue where the background is also black