According to the Metropolitan Museum's website, the signature is on the verso of the drawing, at the lower left, inscribed "P.Brugel" in graphite by a later hand.
Jan did another drawing of the castle while he was in Heidelberg, now known only through a copy in Stuttgart: see Essen/Vienna, p. 426, n. 8. The castle appears from in the background of several versions of Jan's Allegory of Earth from around 1611: Ertz 491-4.
According to Ruby, depicts the northern front of Heidelberg castle before it was finished in the early 1590s. This confirms that Jan’s departure from Antwerp occurred in the late 1580s.