Your example used ・ but clreq says:
着重号用于表示相应文本的强调、着重语气或避免歧义。其形态为标注于文字底端或顶端（横排多在下方〔底端〕、直排多在右侧〔顶端〕）的圆形中黑点，可以为U+25CF BLACK CIRCLE [●]或U+2022 BULLET [•]。
Emphasis marks, also known as emphasis dots, are symbols placed on the line head or line foot to emphasize the text, strengthen the tone, or avoid ambiguity. For horizontal writing mode, emphasis marks are placed under the characters, whereas in vertical writing mode, they are usually placed to the right side of the characters. Both U+25CF BLACK CIRCLE [●] or U+2022 BULLET [•] can work as emphasis marks.
Semantically the 着重号 is similar to emph or strong (personally I’d say it is closer to emph) using a grid to place the dots loses some accessibility. I think emph and putting a bullet inside pdf.artifact("layout") would be better. The outcome will depend on the font though.