It is a bit unusual to ask a question that you already know the answer to, rather than stating a fact, but - hey ho - life's full of surprises.
Anyhow, we've now established that Hergé's name appears on a shop sign in
Le Mystère de la Grande Pyramide.
In order to turn this thread into something more constructive, I'll attempt to fill in a few additional facts.
I think (correct me if I'm wrong) that Jacobs was still working with Hergé around this time (1954-55), embellishing some of the Egyptian tomb paintings in the re-worked
Cigars of the Pharaoh. And we all know (well, we should!) that Hergé pays tribute to Jacobs on the cover (and on page 8 of the book) by including an "E.P. Jacobini" as one of the mummies (who looks like Jacobs, and has his signature bow-tie).
Also, one of the other mummies on the
Cigars cover - Grosgrab - is based on Professor Grossgrabenstein, a character from
Le Mystère de la Grande Pyramide.
So, both men were working on different Ancient Egyptian themed books and thought to pay each other a small compliment in each of them.
And, for anyone that hasn't read them, I think the two-part
Le Mystère de la Grande Pyramide are two of the best Blake and Mortimer books. Highly recommended - and an English edition of the story will be coming out soon, (I hope)!
Moderator Note: For more on the real-life model for Grosgrab/ Grossgrabenstein, the Egyptologist Jean Capart,
see this thread!