score:32
It stands for "Titi filius Titi nepos", meaning "son of Titus and grandson of Titus" (filius and nepos mean son and grandson, respectively).
This is because the consul Titus Flavius Sabinus was the son of the (non-consul) Titus Flavius Sabinus, who was in turn the son of Titus Flavius Petro. So as @SteveBird observed, the abbreivations are "filiation", i.e. the part of the name describing paternity.
Note that we can determine both T.'s stand for Titus because there's a set formula for how these names are abbreviated. In Roman names, the first part, known as praenomen (in examples above, "Titus") are the personal names. However, there were only ever about three dozens of these, and only ten or so were common in the historical record.
As a result, there are standardised abbreviations:
Roman naming conventions are very annoying.
Upvote:7
The personal name in the Roman naming system is composed of several independent elements.
A Roman male name of the late Republic such as
Q. Numerius Q. f. Vel. Rufus comprises the following:
the praenomen or the old individual name (siglum Q = Quintus ),
the gentile or family name (Numerius),
the filiation, which gives the praenomen of the father in the genitive (usually as a siglum) before the abbreviated f(ilius) (Quinti filius 'son of Quintus') and in highly official texts also the praenomen of the grandfather (cf. Fasti consulares, 260 BC: Cn. Cornelius L. f. Cn(aei) n(epos) Scipio Asina),
the indication of the tribus in a defined abbreviation (Vel(inā tribū): abl. of quality), and
the cognomen , which as an individual cognomen was the younger individual name and as a hereditary cognomen served to differentiate the branches (stirpes) of noble families (Gens) (for example, combined in Scipio Asina). Since use of the cognomen was not a universal custom even in the late Republic (for example, it is missing for the victor over the Cimbri, C. Marius [I 1] and the triumvir M. Antonius [I 9]) and the oldest son usually adopted his father’s praenomen, the system did not always permit identification of a person, especially between generations.
However, it generally fulfilled its function superbly even in a large society.
–– The above adapted in formatting from: Rix, Helmut (Freiburg), García-Ramón, José Luis (Cologne), Streck, Michael P. (Munich) and Haas, Volkert (Berlin), “Personal names”, in: Brill’s New Pauly, Antiquity volumes edited by: Hubert Cancik and , Helmuth Schneider, English Edition by: Christine F. Salazar, Classical Tradition volumes edited by: Manfred Landfester, English Edition by: Francis G. Gentry. http://dx.doi.org/10.1163/1574-9347_bnp_e915460
So we see that Wikipedia is a highly official Roman text and as such uses the filiation of father and grandfather of Titus Flavius T.f. T.n. Sabinus, which very creatively were also named Titus Flavius Sabinus (Titus Flavius T.f. Sabinus ), just like a few others…