* Cinq Francs Série 4 301898: This refers to a five-franc note from the "Série 4" (Series 4) of French banknotes, with the specific serial number 301898.
* BO: This likely refers to the Banque de l'Oise, the regional bank for the Oise department of France.
* Regional Emis Sous La Garantie des Communes Occupees Formant le Syndicat Nord Aisne and Oise: This is a lengthy phrase meaning "regional emission under the guarantee of the occupied communes forming the Syndicat Nord Aisne and Oise." This means the note was issued by a consortium of local municipalities in the Nord, Aisne, and Oise departments, which were all under German occupation during the war. This was a way for local authorities to raise funds for necessities while the central government in Paris was not functioning fully.
* Remboursable Dans Les 2 Ans de Signature 12 Decembre 1917: This indicates the note was redeemable (could be exchanged for gold or other legal tender) within two years from the date of its signing, which was December 12, 1917.
In essence, this note was an emergency currency issued by local authorities in occupied northern France during World War I. It was backed by the guarantee of the involved communes and had a limited period of validity.
These notes are of historical interest for collectors, and their value can vary depending on their condition and rarity. If you have one, consider researching its specific characteristics and potential worth.