Businesses often use decals and stickers to communicate to customers which payment methods are available. You can order decals and stickers for Visa and Mastercard through the following links:
Visa: https://merchantsignage.visa.com/. Available in France, Germany, Ireland, Italy, Portugal, Spain and the UK.
Mastercard: https://www.mastercard.com/brandcenter/en/order-decals. Available globally, shipped from the US. Note that international orders may take some time to arrive.