Is there anything more passive-aggressive than a smiley face sticker telling your client to pay their damn invoice? We don’t think so.
Put it on the back of envelopes, or on a client’s Christmas card as a friendly reminder — that 90-day overdue invoice isn’t going to pay itself.
Reminder: you deserve to get paid for your work. If your client gets butthurt that you used this sticker, then maybe they should pay you on time.
While you're at it, buy our red flag sticker. (Because not paying invoices is a huge red flag.)