Health and Safety Executive inspector Steven Simmons-Jacobs told the inquest that the sign could have fallen down "at any time".
It was not properly screwed on, and was held up by small "panel pins", which were not designed to hold the weight of a large sign.
Rainwater had poured on to the wood behind the sign, causing it to buckle, and no one had checked to see if the sign and its fixings were in good condition.
William Hill, Saltwell Signs, which put up the sign, and Acean Builders, which carried out a re-fit, all denied responsibility for checking whether the sign was properly fixed.
Mr Marx' girlfriend, Natalie Chung, said they had planned to get married. The couple had been together for nine years and had been in London for four months.
Miss Chung, with Mr Marx' parents Susan and Allen and two brothers issued a statement after the verdict expressing their grief and criticising William Hill.
"We have been disappointed by the apparent lack of regulation, structured training, or even guidance in the sign-fixing industry and we call on those authorities with the ability to do so, to institute measures to try to prevent such a tragedy ever occurring again," it said.
"Words cannot express adequately the impact of Jacob's death and the grief felt for him. His parents feel a huge loss of their loving, supportive son, and also grieve that they will never see him enjoying the pleasure of his own family, or realise his life potential ...
"Natalie Chung's world was ripped apart and changed forever when Jacob died. The loss of her partner and best friend is a trauma and tragedy she will never understand. "
A William Hill spokesman said checks had been made on all 2500 of its UK stores as a result of Mr Marx' death and a "robust maintenance programme" was in place.
