In DGGNT, I read
5.4.1 Redundant Vocatives as Forward-Pointing Devices
Vocatives and nominatives of address generally are used to identify the “addressee,” the one to whom the writer or speaker is addressing the communication. They typically are used either to identify the intended audience or to signal a switch to a new addressee. The vocatives or nominatives of address are indicated by the G symbol. In Eph 6, the forms of address are needed to clearly identify Paul’s intended audiences as he moves from topic to topic.
Steven E. Runge, Discourse Grammar of the Greek New Testament: A Practical Introduction for Teaching and Exegesis (Bellingham, WA: Lexham Press, 2010), 117.
Symbol G should be a megaphone, but the forum software seemed to reject that.
However, when I hover over the symbol in LDGNT, I see

This seems contradictory.