That is NOT the same as a Medicare ABN and will not suffice to shift financial responsibility for a noncovered service.
You can find links to the forms that are required here: https://www.cms.gov/Medicare/Medicare-General-Information/BNI/ABN.html
And again – the doctor can’t just give a blanket ABN to every patient. So that financial responsibility form you signed way back when no longer applies.
I do think that your doctor could give you an ABN for the injections, and then go ahead and give you the shots (rather than scheduling appointments 6 weeks out) – but you haven’t described that happening. In that case the doctor would be protected.