Thamudic C inscriptions usually open with the phrase wdd 'love' and variants thereof followed by f and a personal name. Scholars have generally treated this phrase as a type of greeting, although the syntactic function of f has not been clear. Winnett (1970) suggested that it should be identified with the Arabic noun fā, the construct of fam "mouth", the entire phrase meaning 'he loved the mouth of so-and-so." Tsafrir (1996) outlined all the variants of this construction but did not offer an explanation for f. A Thamudic C/D inscription -- the short text lacks any diagnostic features to distinguish between the two categories of Thamudic -- from the region of Tabuk published on Twitter by @ahmed666551 may shed some light on its use. Unlike most Thamudic C inscriptions, the wdd f phrase is broken up by the prepositional phrase b-y.
1) Thamudic C inscription published here: https://twitter.com/ahmed666551/status/1451815771114512389?s=20
Reading: wdd by f-mśr
Translation: 'There is love in me for Mśr'
The syntax of this short inscription indicates that wdd is a noun rather than a verb. The prepositional phrase by should be parsed as the locative preposition b 'in' and the first person common singular clitic pronoun, likely vocalized as ya. The inscription suggests that f should be treated as a dative, similar in function to li in Arabic, meaning 'to', 'for'. Its syntax mirrors a previously attested phrase with by in Thamudic D rbt śq by l-kn ʾmt śkrn 'there is much longing in me for Kn the maidservant of Śkrn' (UdhThamD 1 = JSTham 213; Macdonald 2018b). Thus, the present texts conclusively rules out the interpretation of f as a preposition cognate with Arabic fī 'in'.
Thamudic C inscriptions also attest the use of l- in the phrase zt l-PN 'this is for PN', so it is unclear what the difference between the two particles is. It is possible that wdd takes a direct object and that f is therefore a direct object marker. We must await the discovery of longer texts to arbitrate between these two possibilities.
Macdonald, Michael C. A. 2018b. "The Ancient North Arabian and Ancient South Arabian Inscriptions. In The Darb al-Bakrah," edited by Laïla Nehmé . Riyadh: Saudi Commission for Tourism and National Heritage, pp. 227–84
Tsafrir, Nurit. 1996. “New Thamudic inscriptions from the Negev.” Le Muséon 109:79-93.
Winnett, F.V. & Reed, W.L. 1970. Ancient Records from North Arabia. with contributions by J.T. Milik and J. Starcky. (Near and Middle East Series, 6). Toronto: University of Toronto Press.