Would they place a lien on it? Would you get a letter in the mail?
You would definately know. They would serve and or post notice. They can take it but not secretly.
Personal Injury Lawyer
You would know the moment it happens as the federal officers would give you a copy of the notice or post it on your property.
Federal Crime Lawyer
Notice personally and in the county's deed register.
The seizing agency or the US Attorney's Office (depending on the value of the property) will notify all owners and potential claimants known the agency of the seizure by certified mail or publication, and it will file a notice of pending litigation, known as a "lis pendens," with the clerk of the appropriate state court in the county in which the property is located. - Joshua Sabert Lowther, Esq., National Federal Defense Group.
Notice is constitutionally necessary to seize your property. The type of notice is dependent on many factors and procedures.
Of course, every answer or response is based on the information provided in the question asked and requires a much more complete context than is available in this public forum. This answer/response should NOT be relied upon to make any legal decisions. Seek the advice of an experienced Federal and/or state criminal defense attorney in your jurisdiction BEFORE you say or do anything.