The lien notice you got is nothing more than a wide net to secure the real property, or collateral. The steel provider does not necessarily know who has a financial stake in the property, so everyone gets a notice. Say if you as the engineer was not paid, you could theoretically also file a lien for your unpaid fees to secure your right to be paid in the event the property is sold. Anyone owed money that went into increasing the value of the property has a right to lien, but you are required to perfect the lien in order to secure the collateral. If you don't, you can't get your money.
As for whether or not you have to disclose, that's a grayer area. Technically, the lien is against the real property, not the professionals providing services. I would be tempted not to mention it for your run-of-the-mill projects. For huge government projects where attorneys are already scrutinizing the contract, I would have them do a once-over.
BTW, this subject is covered quite extensively on the architect's exam. We are required to know this topic in a broad sense.
If you are offended by the things I say, imagine the stuff I hold back.