。、♪
I'm in the rankings. If you like what you see, click for me ♪
Literal
Ranking participation-middle [copula-です]. Interesting-[if-ば], click ♪
Blog-ranking-widget register, common on early-2000s Japanese personal blogs, which linked to ranking aggregator sites and asked visitors to click a button to vote. 参加中 uses the ~中 suffix 'in the middle of, during' attached to a noun. ポチッと is a mimetic for the sound/feel of pressing a button — 'click!' — routinely used in casual writing to invite button-presses. The ♪ music-note symbol stylizes the request as light and cheerful. The sentence fragment ポチッと has the implicit 'please' or 'click it' left unsaid.