As someone who has studied Harrison quite intensely I would hope to give an at least well reasoned view on this.
I would argue that this stanza highlights the way in which our perception and understanding of symbols, words and actions are determined predominantly by changing social norms dictated by the upper classes. As 'no-one clamoured in the press for its removal' Harrison highlights the arbitrary nature of this symbols; we have an example of graffiti that was an approved of set against the same symbol that was frowned upon-in this case the Vs the skinhead draws on graves. The symbol stays the same, what changes is society-one reading might be that Harrison is suggesting the upper classes more keenly attack the actions of the lower classes in the present compared to his youth, but I would say Harrison is making a more general point about the way we understand meaning.
Throughout his works, Harrison addresses the fact that over time our perception of language has changed according to social norms. For example, in 'Them and [uz]' Harrison brings attention to the fact that 'all poetry...'s been dubbed by [Λs] into RP' here Harrison highlights the fact that voices that were originally demotic or working class e.g. Keats and Wordsworth are now perceived as upper class voices because the English upper class ([Λs]) have 'dubbed' them to suit their purposes. The poetry is the same, much like the V, but our understanding of it has changed due to social norms and views on what kinds of socioeconomic classes get to produce and consume certain forms of art. It may be said that by doing this, Harrison highlights the way in which symbols and words may be appropriated by those in power-the fact that V is used with such versatility in the poem, and with so many meanings, shows how meaning is contextual in Harrison's view, for better or for worse.
Furthermore, Harrison may be addressing the fact that certain acts are deemed more acceptable in wartime or times of supposed crisis. The act of graffiti in the poem may reflect other acts that 'in wartime' are acceptable. Therefore Harrison, who is an established War Poet, may be addressing briefly the hypocrisy of a society that condemns some acts in peacetime but allows in wartime. Considering that Harrison's poetry is at times very clearly shaped by his experience of seeing war crimes and the use of nuclear weapons in his childhood, this could be a nod to one of Harrison's main sources of anger and concern.
You are free to completely reject these readings of course, and although there is not a great amount of critical work on Harrison; I'd recommend for this particular theme reading Harrison's School of Eloquence (1978), watching the film poem version of V and to get a particular sense of the way in which he reclaims texts at least taking a casual glance at some of his dramaturgy; The Mysteries (1985), The Labourers of Herakles (1996) and The Trackers of Oxyrhynchus (1988) all give a flavour of this. In terms of literary criticism, Holocaust Poetry: Awkward Poetics in the Work of Sylvia Plath, Geoffrey Hill, Tony Harrison and Ted Hughes by Anthony Rowland is well argued and, if you can access it, Public Poetry in the Work of Tony Harrison by Lenka Filopova is a good overview.