Is this an old TPR valve. If so, is it safe?
Likely pressure only.
And it is very old.
Is this a steam boiler?
Yes. Steam boiler. Probably original with house - 1950’s. Make sense?
Yes it does.
I would recommend service by a qualified heating contractor specializing in steam boilers.
50 years is not that unusual but it is likely to be inefficient and needs periodic tune ups especially if it is oil fired.
Pretty much how I reported it. Thanks.