The 300A is the one recordkeeping form that goes on the wall, and the rules about it are precise.
Before you post. At the end of each calendar year the employer must review the OSHA 300 Log to verify the entries are complete and accurate, create the annual summary, certify it, and post it (29 CFR 1904.32(a)). The review must be as extensive as necessary to make sure the entries are complete and correct (29 CFR 1904.32(b)(1)). To complete the summary, total the columns on the Log — if there were no recordable cases, enter zeros for each column total — and fill in the establishment information (29 CFR 1904.32(b)(2)). An establishment with zero cases still posts a 300A.
Who certifies. A company executive must certify that he or she has examined the 300 Log and reasonably believes, based on knowledge of the process by which the information was recorded, that the summary is correct and complete (29 CFR 1904.32(b)(3)). The executive must be an owner of the company, an officer of the corporation, the highest ranking company official working at the establishment, or that official's immediate supervisor (29 CFR 1904.32(b)(4)). The safety manager's signature does not satisfy this unless the safety manager is also one of those people.
Where and when. Post a copy in each establishment in a conspicuous place or places where notices to employees are customarily posted, and make sure it is not altered, defaced or covered (29 CFR 1904.32(b)(5)). Post no later than February 1 of the year following the year covered and keep it in place until April 30 (29 CFR 1904.32(b)(6)).
Separately. Establishments covered by the electronic reporting rule also submit the 300A data to OSHA by March 2 (29 CFR 1904.41(c)); posting and submitting are two different obligations.
The three-month window exists so that employees who were on the payroll during the year see the totals. Taking it down on March 1 because the submission is done is a common mistake.