618

618 is a recurring number in Gravity Falls. It is based off the date of June 18th, which is the birthday of series creator Alex Hirsch. 618 is also used as show's main production code.

618 Instances
The following are sightings of 618 in the show:
 * The show's main production code is 618.
 * e.g. Dipper and Mabel's rough model sheets are labeled "618G99.01."
 * e.g. An episode production code starts with 618, such as "618G-107" for "Tourist Trapped."
 * The Mystery Shack's address is 618, Gopher Road.
 * The cash register of the Gift Shop is often by default $6.18.
 * On Tumbleweed Terror the number in the barrel is 618.
 * Gideon Gleeful's school ID number.
 * One of the blocks a baby chews on in Baby Fights has the numbers 6, 1, and 8.