Slightly confused as to what this wire is. Is this power? This house was built in the 1950s and I believe had knob and tube wiring. However I noticed that I do have a service drop for electrical on my roof.
Generally power poles have a tier system.
(optional) Top top top = lightning arrestor cable (grounded) placed so lighting will hit it instead of the power lines
(optional) Top top = high voltage (note fat or stacked insulators) and often 2-wire, but can be 3-wire, and on a cross-bar. You will often see them go to weird fixtures, such as the cutout switches on the 2nd pole.
Upper = 120/240V AC power distribution (3 wires) on short insulators usually on a crossbar. All the triplex service drops to houses will come off this.
Middle = Telephone
Bottom = cable TV
On your photo, the standard telephone splice boxes can be seen on the middle tier.
Yours is going to the bottom tier, so it's cable TV.